TTree

继承 TNamed, TAttLine, TAttFill, TAttMarker

A TTree object is a list of TBranch. To Create a TTree object one must:

  • Create the TTree header via the TTree constructor
  • Call the TBranch constructor for every branch.

To Fill this object, use member function Fill with no parameters. The Fill function loops on all defined TBranch.

function Scan()

The options string can contains the following parameters:

  • lenmax=dd
    • Where 'dd' is the maximum number of elements per array that should be printed. If 'dd' is 0, all elements are printed (this is the default)
  • colsize=ss
    • Where 'ss' will be used as the default size for all the column. If this options is not specified, the default column size is 9
  • precision=pp
    • Where 'pp' will be used as the default 'precision' for the printing format.
  • col=xxx
    • Where 'xxx' is colon (:) delimited list of printing format for each column. The format string should follow the printf format specification. The value given will be prefixed by % and, if no conversion specifier is given, will be suffixed by the letter g. before being passed to fprintf. If no format is specified for a column, the default is used (aka ${colsize}.${precision}g )

function Draw()

  • Entry$:
    • A TTree::Draw formula can use the special variable Entry$ to access the entry number being read.

class

   // Used as the max value for any TTree range operation.
   static constexpr Long64_t kMaxEntries = TVirtualTreePlayer::kMaxEntries;

   // SetBranchAddress return values
   enum ESetBranchAddressStatus {
      kMissingBranch = -5,
      kInternalError = -4,
      kMissingCompiledCollectionProxy = -3,
      kMismatch = -2,
      kClassMismatch = -1,
      kMatch = 0,
      kMatchConversion = 1,
      kMatchConversionCollection = 2,
      kMakeClass = 3,
      kVoidPtr = 4,
      kNoCheck = 5
   };

   // TTree status bits
   enum {
      kForceRead   = BIT(11),
      kCircular    = BIT(12)
   };

   // Split level modifier
   enum {
      kSplitCollectionOfPointers = 100
   };

   class TClusterIterator
   {
   private:
      TTree    *fTree;        // TTree upon which we are iterating.
      Int_t    fClusterRange; // Which cluster range are we looking at.
      Long64_t fStartEntry;   // Where does the cluster start.
      Long64_t fNextEntry;    // Where does the cluster end (exclusive).

      Long64_t GetEstimatedClusterSize();

   protected:
      friend class TTree;
      TClusterIterator(TTree *tree, Long64_t firstEntry);

   public:
      // Intentionally used the default copy constructor and default destructor
      // as the TClusterIterator does not own the TTree.
      //  TClusterIterator(const TClusterIterator&);
      // ~TClusterIterator();

      // No public constructors, the iterator must be
      // created via TTree::GetClusterIterator

      // Move on to the next cluster and return the starting entry
      // of this next cluster
      Long64_t Next();

      // Return the start entry of the current cluster.
      Long64_t GetStartEntry() {
         return fStartEntry;
      }

      // Return the first entry of the next cluster.
      Long64_t GetNextEntry() {
         return fNextEntry;
      }

      Long64_t operator()() { return Next(); }
   };

   TTree();
/// Default constructor and I/O constructor.
/// Note: We do *not* insert ourself into the current directory.

   TTree(const char* name, const char* title, Int_t splitlevel = 99);
/// Normal tree constructor.
/// The tree is created in the current directory.
/// Use the various functions Branch below to add branches to this tree.
/// If the first character of title is a "/", the function assumes a folder name.
/// In this case, it creates automatically branches following the folder hierarchy.
/// splitlevel may be used in this case to control the split level.

   virtual ~TTree();

   virtual Int_t           AddBranchToCache(const char *bname, Bool_t subbranches = kFALSE);
/// Add branch with name bname to the Tree cache.
/// If bname="*" all branches are added to the cache.
/// if subbranches is true all the branches of the subbranches are
/// also put to the cache.
/// Returns:
/// - 0 branch added or already included
/// - -1 on error

   virtual Int_t           AddBranchToCache(TBranch *branch,   Bool_t subbranches = kFALSE);
/// Add branch b to the Tree cache.
/// if subbranches is true all the branches of the subbranches are
/// also put to the cache.
/// Returns:
/// - 0 branch added or already included
/// - -1 on error

   virtual Int_t           DropBranchFromCache(const char *bname, Bool_t subbranches = kFALSE);
/// Remove the branch with name 'bname' from the Tree cache.
/// If bname="*" all branches are removed from the cache.
/// if subbranches is true all the branches of the subbranches are
/// also removed from the cache.
/// Returns:
/// - 0 branch dropped or not in cache
/// - -1 on error

   virtual Int_t           DropBranchFromCache(TBranch *branch,   Bool_t subbranches = kFALSE);
/// Remove the branch b from the Tree cache.
/// if subbranches is true all the branches of the subbranches are
/// also removed from the cache.
/// Returns:
/// - 0 branch dropped or not in cache
/// - -1 on error

   virtual TFriendElement *AddFriend(const char* treename, const char* filename = "");
/// Add a TFriendElement to the list of friends.
/// This function:
/// - opens a file if filename is specified
/// - reads a Tree with name treename from the file (current directory)
/// - adds the Tree to the list of friends
/// see other AddFriend functions
/// A TFriendElement TF describes a TTree object TF in a file.
/// When a TFriendElement TF is added to the the list of friends of an
/// existing TTree T, any variable from TF can be referenced in a query
/// to T.
///   A tree keeps a list of friends. In the context of a tree (or a chain),
/// friendship means unrestricted access to the friends data. In this way
/// it is much like adding another branch to the tree without taking the risk
/// of damaging it. To add a friend to the list, you can use the TTree::AddFriend
/// method.  The tree in the diagram below has two friends (friend_tree1 and
/// friend_tree2) and now has access to the variables a,b,c,i,j,k,l and m.
/// The AddFriend method has two parameters, the first is the tree name and the
/// second is the name of the ROOT file where the friend tree is saved.
/// AddFriend automatically opens the friend file. If no file name is given,
/// the tree called ft1 is assumed to be in the same file as the original tree.
/// tree.AddFriend("ft1","friendfile1.root");
/// If the friend tree has the same name as the original tree, you can give it
/// an alias in the context of the friendship:
/// tree.AddFriend("tree1 = tree","friendfile1.root");
/// Once the tree has friends, we can use TTree::Draw as if the friend's
/// variables were in the original tree. To specify which tree to use in
/// the Draw method, use the syntax:
/// ~~~ {.cpp}
///     <treeName>.<branchname>.<varname>
/// ~~~
/// If the variablename is enough to uniquely identify the variable, you can
/// leave out the tree and/or branch name.
/// For example, these commands generate a 3-d scatter plot of variable "var"
/// in the TTree tree versus variable v1 in TTree ft1 versus variable v2 in
/// TTree ft2.
/// ~~~ {.cpp}
///     tree.AddFriend("ft1","friendfile1.root");
///     tree.AddFriend("ft2","friendfile2.root");
///     tree.Draw("var:ft1.v1:ft2.v2");
/// ~~~
/// When AddFriend is called, the ROOT file is automatically opened and the
/// friend tree (ft1) is read into memory. The new friend (ft1) is added to
/// the list of friends of tree.
/// The number of entries in the friend must be equal or greater to the number
/// of entries of the original tree. If the friend tree has fewer entries a
/// warning is given and the missing entries are not included in the histogram.
/// To retrieve the list of friends from a tree use TTree::GetListOfFriends.
/// When the tree is written to file (TTree::Write), the friends list is saved
/// with it. And when the tree is retrieved, the trees on the friends list are
/// also retrieved and the friendship restored.
/// When a tree is deleted, the elements of the friend list are also deleted.
/// It is possible to declare a friend tree that has the same internal
/// structure (same branches and leaves) as the original tree, and compare the
/// same values by specifying the tree.
/// ~~~ {.cpp}
///     tree.Draw("var:ft1.var:ft2.var")
/// ~~~

   virtual TFriendElement *AddFriend(const char* treename, TFile* file);
/// Add a TFriendElement to the list of friends.
/// The TFile is managed by the user (e.g. the user must delete the file).
/// For complete description see AddFriend(const char *, const char *).
/// This function:
/// - reads a Tree with name treename from the file
/// - adds the Tree to the list of friends

   virtual TFriendElement *AddFriend(TTree* tree, const char* alias = "", Bool_t warn = kFALSE);
/// Add a TFriendElement to the list of friends.
/// The TTree is managed by the user (e.g., the user must delete the file).
/// For a complete description see AddFriend(const char *, const char *).

   virtual void            AddTotBytes(Int_t tot) { fTotBytes += tot; }
   virtual void            AddZipBytes(Int_t zip) { fZipBytes += zip; }
   virtual Long64_t        AutoSave(Option_t* option = "");
// AutoSave tree header every fAutoSave bytes.
//   When large Trees are produced, it is safe to activate the AutoSave
//   procedure. Some branches may have buffers holding many entries.
//   AutoSave is automatically called by TTree::Fill when the number of bytes
//   generated since the previous AutoSave is greater than fAutoSave bytes.
//   This function may also be invoked by the user, for example every
//   N entries.
//   Each AutoSave generates a new key on the file.
//   Once the key with the tree header has been written, the previous cycle
//   (if any) is deleted.
//   Note that calling TTree::AutoSave too frequently (or similarly calling
//   TTree::SetAutoSave with a small value) is an expensive operation.
//   You should make tests for your own application to find a compromise
//   between speed and the quantity of information you may loose in case of
//   a job crash.
//   In case your program crashes before closing the file holding this tree,
//   the file will be automatically recovered when you will connect the file
//   in UPDATE mode.
//   The Tree will be recovered at the status corresponding to the last AutoSave.
//   if option contains "SaveSelf", gDirectory->SaveSelf() is called.
//   This allows another process to analyze the Tree while the Tree is being filled.
//   if option contains "FlushBaskets", TTree::FlushBaskets is called and all
//   the current basket are closed-out and written to disk individually.
//   By default the previous header is deleted after having written the new header.
//   if option contains "Overwrite", the previous Tree header is deleted
//   before written the new header. This option is slightly faster, but
//   the default option is safer in case of a problem (disk quota exceeded)
//   when writing the new header.
//   The function returns the number of bytes written to the file.
//   if the number of bytes is null, an error has occurred while writing
//   the header to the file.

   virtual Int_t           Branch(TCollection* list, Int_t bufsize = 32000, Int_t splitlevel = 99, const char* name = "");
/// Create one branch for each element in the collection.
/// Each entry in the collection becomes a top level branch if the
/// corresponding class is not a collection. If it is a collection, the entry
/// in the collection becomes in turn top level branches, etc.
/// The splitlevel is decreased by 1 every time a new collection is found.
/// For example if list is a TObjArray*
///   - if splitlevel = 1, one top level branch is created for each element
///      of the TObjArray.
///   - if splitlevel = 2, one top level branch is created for each array element.
///     if, in turn, one of the array elements is a TCollection, one top level
///     branch will be created for each element of this collection.
/// In case a collection element is a TClonesArray, the special Tree constructor
/// for TClonesArray is called.
/// The collection itself cannot be a TClonesArray.
/// The function returns the total number of branches created.
/// If name is given, all branch names will be prefixed with name_.
/// IMPORTANT NOTE1: This function should not be called with splitlevel < 1.
/// IMPORTANT NOTE2: The branches created by this function will have names
/// corresponding to the collection or object names. It is important
/// to give names to collections to avoid misleading branch names or
/// identical branch names. By default collections have a name equal to
/// the corresponding class name, e.g. the default name for a TList is "TList".
/// And in general in any cases two or more master branches contain subbranches
/// with identical names, one must add a "." (dot) character at the end
/// of the master branch name. This will force the name of the subbranch
/// to be master.subbranch instead of simply subbranch.
/// This situation happens when the top level object (say event)
/// has two or more members referencing the same class.
/// For example, if a Tree has two branches B1 and B2 corresponding
/// to objects of the same class MyClass, one can do:
/// ~~~ {.cpp}
///     tree.Branch("B1.","MyClass",&b1,8000,1);
///     tree.Branch("B2.","MyClass",&b2,8000,1);
/// ~~~
/// if MyClass has 3 members a,b,c, the two instructions above will generate
/// subbranches called B1.a, B1.b ,B1.c, B2.a, B2.b, B2.c

   virtual Int_t           Branch(TList* list, Int_t bufsize = 32000, Int_t splitlevel = 99);
/// Deprecated function. Use next function instead.

   virtual Int_t           Branch(const char* folder, Int_t bufsize = 32000, Int_t splitlevel = 99);
/// Create one branch for each element in the folder.
/// Returns the total number of branches created.

   virtual TBranch        *Branch(const char* name, void* address, const char* leaflist, Int_t bufsize = 32000);
/// Create a new TTree Branch.
/// This Branch constructor is provided to support non-objects in
/// a Tree. The variables described in leaflist may be simple
/// variables or structures.  // See the two following
/// constructors for writing objects in a Tree.
/// By default the branch buffers are stored in the same file as the Tree.
/// use TBranch::SetFile to specify a different file
///    * address is the address of the first item of a structure.
///    * leaflist is the concatenation of all the variable names and types
///      separated by a colon character :
///      The variable name and the variable type are separated by a slash (/).
///      The variable type may be 0,1 or 2 characters. If no type is given,
///      the type of the variable is assumed to be the same as the previous
///      variable. If the first variable does not have a type, it is assumed
///      of type F by default. The list of currently supported types is given below:
///         - C : a character string terminated by the 0 character
///         - B : an 8 bit signed integer (Char_t)
///         - b : an 8 bit unsigned integer (UChar_t)
///         - S : a 16 bit signed integer (Short_t)
///         - s : a 16 bit unsigned integer (UShort_t)
///         - I : a 32 bit signed integer (Int_t)
///         - i : a 32 bit unsigned integer (UInt_t)
///         - F : a 32 bit floating point (Float_t)
///         - D : a 64 bit floating point (Double_t)
///         - L : a 64 bit signed integer (Long64_t)
///         - l : a 64 bit unsigned integer (ULong64_t)
///         - O : [the letter 'o', not a zero] a boolean (Bool_t)
///      Arrays of values are supported with the following syntax:
///         - If leaf name has the form var[nelem], where nelem is alphanumeric, then
///           if nelem is a leaf name, it is used as the variable size of the array,
///           otherwise return 0.
///         - If leaf name has the form var[nelem], where nelem is a non-negative integer, then
///           it is used as the fixed size of the array.
///         - If leaf name has the form of a multi-dimensional array (e.g. var[nelem][nelem2])
///           where nelem and nelem2 are non-negative integer) then
///           it is used as a 2 dimensional array of fixed size.
///      Any of other form is not supported.
/// Note that the TTree will assume that all the item are contiguous in memory.
/// On some platform, this is not always true of the member of a struct or a class,
/// due to padding and alignment.  Sorting your data member in order of decreasing
/// sizeof usually leads to their being contiguous in memory.
///    * bufsize is the buffer size in bytes for this branch
///      The default value is 32000 bytes and should be ok for most cases.
///      You can specify a larger value (e.g. 256000) if your Tree is not split
///      and each entry is large (Megabytes)
///      A small value for bufsize is optimum if you intend to access
///      the entries in the Tree randomly and your Tree is in split mode.

           TBranch        *Branch(const char* name, char* address, const char* leaflist, Int_t bufsize = 32000)
   {
      // Overload to avoid confusion between this signature and the template instance.
      return Branch(name,(void*)address,leaflist,bufsize);
   }
   TBranch        *Branch(const char* name, Long_t address, const char* leaflist, Int_t bufsize = 32000)
   {
      // Overload to avoid confusion between this signature and the template instance.
      return Branch(name,(void*)address,leaflist,bufsize);
   }
   TBranch        *Branch(const char* name, int address, const char* leaflist, Int_t bufsize = 32000)
   {
      // Overload to avoid confusion between this signature and the template instance.
      return Branch(name,(void*)(Long_t)address,leaflist,bufsize);
   }
#if !defined(__CINT__)
   virtual TBranch        *Branch(const char* name, const char* classname, void* addobj, Int_t bufsize = 32000, Int_t splitlevel = 99);
/// Create a new branch with the object of class classname at address addobj.
/// WARNING:
/// Starting with Root version 3.01, the Branch function uses the new style
/// branches (TBranchElement). To get the old behaviour, you can:
///   - call BranchOld or
///   - call TTree::SetBranchStyle(0)
/// Note that with the new style, classname does not need to derive from TObject.
/// It must derived from TObject if the branch style has been set to 0 (old)
/// Note: See the comments in TBranchElement::SetAddress() for a more
///       detailed discussion of the meaning of the addobj parameter in
///       the case of new-style branches.
/// Use splitlevel < 0 instead of splitlevel=0 when the class
/// has a custom Streamer
/// Note: if the split level is set to the default (99),  TTree::Branch will
/// not issue a warning if the class can not be split.

#endif
   template <class T> TBranch *Branch(const char* name, const char* classname, T* obj, Int_t bufsize = 32000, Int_t splitlevel = 99)
   {
      // See BranchImpRed for details. Here we __ignore
      return BranchImpRef(name, classname, TBuffer::GetClass(typeid(T)), obj, bufsize, splitlevel);
   }
   template <class T> TBranch *Branch(const char* name, const char* classname, T** addobj, Int_t bufsize = 32000, Int_t splitlevel = 99)
   {
      // See BranchImp for details
      return BranchImp(name, classname, TBuffer::GetClass(typeid(T)), addobj, bufsize, splitlevel);
   }
   template <class T> TBranch *Branch(const char* name, T** addobj, Int_t bufsize = 32000, Int_t splitlevel = 99)
   {
      // See BranchImp for details
      return BranchImp(name, TBuffer::GetClass(typeid(T)), addobj, bufsize, splitlevel);
   }
   template <class T> TBranch *Branch(const char* name, T* obj, Int_t bufsize = 32000, Int_t splitlevel = 99)
   {
      // See BranchImp for details
      return BranchImpRef(name, TBuffer::GetClass(typeid(T)), TDataType::GetType(typeid(T)), obj, bufsize, splitlevel);
   }
   virtual TBranch        *Bronch(const char* name, const char* classname, void* addobj, Int_t bufsize = 32000, Int_t splitlevel = 99);
/// Create a new TTree BranchElement.
/// ## WARNING about this new function
/// This function is designed to replace the internal
/// implementation of the old TTree::Branch (whose implementation
/// has been moved to BranchOld).
/// NOTE: The 'Bronch' method supports only one possible calls
/// signature (where the object type has to be specified
/// explicitly and the address must be the address of a pointer).
/// For more flexibility use 'Branch'.  Use Bronch only in (rare)
/// cases (likely to be legacy cases) where both the new and old
/// implementation of Branch needs to be used at the same time.
/// This function is far more powerful than the old Branch
/// function.  It supports the full C++, including STL and has
/// the same behaviour in split or non-split mode. classname does
/// not have to derive from TObject.  The function is based on
/// the new TStreamerInfo.
/// Build a TBranchElement for an object of class classname.
/// addr is the address of a pointer to an object of class
/// classname.  The class dictionary must be available (ClassDef
/// in class header).
/// Note: See the comments in TBranchElement::SetAddress() for a more
///       detailed discussion of the meaning of the addr parameter.
/// This option requires access to the library where the
/// corresponding class is defined. Accessing one single data
/// member in the object implies reading the full object.
/// By default the branch buffers are stored in the same file as the Tree.
/// use TBranch::SetFile to specify a different file
/// IMPORTANT NOTE about branch names:
/// In case two or more master branches contain subbranches with
/// identical names, one must add a "." (dot) character at the end
/// of the master branch name. This will force the name of the subbranch
/// to be master.subbranch instead of simply subbranch.
/// This situation happens when the top level object (say event)
/// has two or more members referencing the same class.
/// For example, if a Tree has two branches B1 and B2 corresponding
/// to objects of the same class MyClass, one can do:
/// ~~~ {.cpp}
///     tree.Branch("B1.","MyClass",&b1,8000,1);
///     tree.Branch("B2.","MyClass",&b2,8000,1);
/// ~~~
/// if MyClass has 3 members a,b,c, the two instructions above will generate
/// subbranches called B1.a, B1.b ,B1.c, B2.a, B2.b, B2.c
/// bufsize is the buffer size in bytes for this branch
/// The default value is 32000 bytes and should be ok for most cases.
/// You can specify a larger value (e.g. 256000) if your Tree is not split
/// and each entry is large (Megabytes)
/// A small value for bufsize is optimum if you intend to access
/// the entries in the Tree randomly and your Tree is in split mode.
/// Use splitlevel < 0 instead of splitlevel=0 when the class
/// has a custom Streamer
/// Note: if the split level is set to the default (99),  TTree::Branch will
/// not issue a warning if the class can not be split.

   virtual TBranch        *BranchOld(const char* name, const char* classname, void* addobj, Int_t bufsize = 32000, Int_t splitlevel = 1);
/// Create a new TTree BranchObject.
/// Build a TBranchObject for an object of class classname.
/// addobj is the address of a pointer to an object of class classname.
/// IMPORTANT: classname must derive from TObject.
/// The class dictionary must be available (ClassDef in class header).
/// This option requires access to the library where the corresponding class
/// is defined. Accessing one single data member in the object implies
/// reading the full object.
/// See the next Branch constructor for a more efficient storage
/// in case the entry consists of arrays of identical objects.
/// By default the branch buffers are stored in the same file as the Tree.
/// use TBranch::SetFile to specify a different file
/// IMPORTANT NOTE about branch names:
/// In case two or more master branches contain subbranches with
/// identical names, one must add a "." (dot) character at the end
/// of the master branch name. This will force the name of the subbranch
/// to be master.subbranch instead of simply subbranch.
/// This situation happens when the top level object (say event)
/// has two or more members referencing the same class.
/// For example, if a Tree has two branches B1 and B2 corresponding
/// to objects of the same class MyClass, one can do:
/// ~~~ {.cpp}
///     tree.Branch("B1.","MyClass",&b1,8000,1);
///     tree.Branch("B2.","MyClass",&b2,8000,1);
/// ~~~
/// if MyClass has 3 members a,b,c, the two instructions above will generate
/// subbranches called B1.a, B1.b ,B1.c, B2.a, B2.b, B2.c
/// bufsize is the buffer size in bytes for this branch
/// The default value is 32000 bytes and should be ok for most cases.
/// You can specify a larger value (e.g. 256000) if your Tree is not split
/// and each entry is large (Megabytes)
/// A small value for bufsize is optimum if you intend to access
/// the entries in the Tree randomly and your Tree is in split mode.

   virtual TBranch        *BranchRef();
/// Build the optional branch supporting the TRefTable.
/// This branch will keep all the information to find the branches
/// containing referenced objects.
/// At each Tree::Fill, the branch numbers containing the
/// referenced objects are saved to the TBranchRef basket.
/// When the Tree header is saved (via TTree::Write), the branch
/// is saved keeping the information with the pointers to the branches
/// having referenced objects.

   virtual void            Browse(TBrowser*);/// Browse content of the TTree.
   virtual Int_t           BuildIndex(const char* majorname, const char* minorname = "0");
/// Build a Tree Index (default is TTreeIndex).
/// See a description of the parameters and functionality in
/// TTreeIndex::TTreeIndex().
/// The return value is the number of entries in the Index (< 0 indicates failure).
/// A TTreeIndex object pointed by fTreeIndex is created.
/// This object will be automatically deleted by the TTree destructor.
/// See also comments in TTree::SetTreeIndex().

   TStreamerInfo          *BuildStreamerInfo(TClass* cl, void* pointer = 0, Bool_t canOptimize = kTRUE);
/// Build StreamerInfo for class cl.
/// pointer is an optional argument that may contain a pointer to an object of cl.

   virtual TFile          *ChangeFile(TFile* file);
/// Called by TTree::Fill() when file has reached its maximum fgMaxTreeSize.
/// Create a new file. If the original file is named "myfile.root",
/// subsequent files are named "myfile_1.root", "myfile_2.root", etc.
/// Returns a pointer to the new file.
/// Currently, the automatic change of file is restricted
/// to the case where the tree is in the top level directory.
/// The file should not contain sub-directories.
/// Before switching to a new file, the tree header is written
/// to the current file, then the current file is closed.
/// To process the multiple files created by ChangeFile, one must use
/// a TChain.
/// The new file name has a suffix "_N" where N is equal to fFileNumber+1.
/// By default a Root session starts with fFileNumber=0. One can set
/// fFileNumber to a different value via TTree::SetFileNumber.
/// In case a file named "_N" already exists, the function will try
/// a file named "__N", then "___N", etc.
/// fgMaxTreeSize can be set via the static function TTree::SetMaxTreeSize.
/// The default value of fgMaxTreeSize is 100 Gigabytes.
/// If the current file contains other objects like TH1 and TTree,
/// these objects are automatically moved to the new file.
/// IMPORTANT NOTE:
/// Be careful when writing the final Tree header to the file!
/// Don't do:
/// ~~~ {.cpp}
///     TFile *file = new TFile("myfile.root","recreate");
///     TTree *T = new TTree("T","title");
///     T->Fill(); //loop
///     file->Write();
///     file->Close();
///~~~
/// but do the following:
///~~~ {.cpp}
///     TFile *file = new TFile("myfile.root","recreate");
///     TTree *T = new TTree("T","title");
///     T->Fill(); //loop
///     file = T->GetCurrentFile(); //to get the pointer to the current file
///     file->Write();
///     file->Close();
/// ~~~

   virtual TTree          *CloneTree(Long64_t nentries = -1, Option_t* option = "");
/// Create a clone of this tree and copy nentries.
/// By default copy all entries.
/// The compression level of the cloned tree is set to the destination
/// file's compression level.
/// NOTE: Only active branches are copied.
/// NOTE: If the TTree is a TChain, the structure of the first TTree
///       is used for the copy.
/// IMPORTANT: The cloned tree stays connected with this tree until
///            this tree is deleted. In particular, any changes in
///            branch addresses in this tree are forwarded to the
///            clone trees, unless a branch in a clone tree has had
///            its address changed, in which case that change stays in
///            effect. When this tree is deleted, all the addresses of
///            the cloned tree are reset to their default values.
/// If 'option' contains the word 'fast' and nentries is -1, the
/// cloning will be done without unzipping or unstreaming the baskets
/// (i.e., a direct copy of the raw bytes on disk).
///
/// When 'fast' is specified, 'option' can also contain a sorting
/// order for the baskets in the output file.
/// There are currently 3 supported sorting order:
/// - SortBasketsByOffset (the default)
/// - SortBasketsByBranch
/// - SortBasketsByEntry
/// When using SortBasketsByOffset the baskets are written in the
/// output file in the same order as in the original file (i.e. the
/// baskets are sorted by their offset in the original file; Usually
/// this also means that the baskets are sorted by the index/number of
/// the _last_ entry they contain)
/// When using SortBasketsByBranch all the baskets of each individual
/// branches are stored contiguously. This tends to optimize reading
/// speed when reading a small number (1->5) of branches, since all
/// their baskets will be clustered together instead of being spread
/// across the file. However it might decrease the performance when
/// reading more branches (or the full entry).
/// When using SortBasketsByEntry the baskets with the lowest starting
/// entry are written first. (i.e. the baskets are sorted by the
/// index/number of the first entry they contain). This means that on
/// the file the baskets will be in the order in which they will be
/// needed when reading the whole tree sequentially.
/// For examples of CloneTree, see tutorials:
/// - copytree:
///     A macro to copy a subset of a TTree to a new TTree.
///     The input file has been generated by the program in
///     $ROOTSYS/test/Event with: Event 1000 1 1 1
/// - copytree2:
///     A macro to copy a subset of a TTree to a new TTree.
///     One branch of the new Tree is written to a separate file.
///     The input file has been generated by the program in
///     $ROOTSYS/test/Event with: Event 1000 1 1 1

   virtual void            CopyAddresses(TTree*,Bool_t undo = kFALSE);
/// Set branch addresses of passed tree equal to ours.
/// If undo is true, reset the branch address instead of copying them.
/// This insures 'separation' of a cloned tree from its original

   virtual Long64_t        CopyEntries(TTree* tree, Long64_t nentries = -1, Option_t *option = "");
/// Copy nentries from given tree to this tree.
/// This routines assumes that the branches that intended to be copied are
/// already connected.   The typical case is that this tree was created using
/// tree->CloneTree(0).
/// By default copy all entries.
/// Returns number of bytes copied to this tree.
/// If 'option' contains the word 'fast' and nentries is -1, the cloning will be
/// done without unzipping or unstreaming the baskets (i.e., a direct copy of the
/// raw bytes on disk).
/// When 'fast' is specified, 'option' can also contains a sorting order for the
/// baskets in the output file.
/// There are currently 3 supported sorting order:
/// - SortBasketsByOffset (the default)
/// - SortBasketsByBranch
/// - SortBasketsByEntry
/// See TTree::CloneTree for a detailed explanation of the semantics of these 3 options.
/// If the tree or any of the underlying tree of the chain has an index, that index and any
/// index in the subsequent underlying TTree objects will be merged.
/// There are currently three 'options' to control this merging:
/// - NoIndex             : all the TTreeIndex object are dropped.
/// - DropIndexOnError    : if any of the underlying TTree object do no have a TTreeIndex,
///                          they are all dropped.
/// - AsIsIndexOnError [default]: In case of missing TTreeIndex, the resulting TTree index has gaps.
/// - BuildIndexOnError : If any of the underlying TTree objects do not have a TTreeIndex,
///                          all TTreeIndex are 'ignored' and the missing piece are rebuilt.

   virtual TTree          *CopyTree(const char* selection, Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0);
/// Copy a tree with selection.
/// IMPORTANT:
/// The returned copied tree stays connected with the original tree
/// until the original tree is deleted.  In particular, any changes
/// to the branch addresses in the original tree are also made to
/// the copied tree.  Any changes made to the branch addresses of the
/// copied tree are overridden anytime the original tree changes its
/// branch addresses.  When the original tree is deleted, all the
/// branch addresses of the copied tree are set to zero.
///
/// For examples of CopyTree, see the tutorials:
/// - copytree:
/// Example macro to copy a subset of a tree to a new tree.
/// The input file was generated by running the program in
/// $ROOTSYS/test/Event in this way:
/// ~~~ {.cpp}
///     ./Event 1000 1 1 1
/// ~~~
/// - copytree2
/// Example macro to copy a subset of a tree to a new tree.
/// One branch of the new tree is written to a separate file.
/// The input file was generated by running the program in
/// $ROOTSYS/test/Event in this way:
/// ~~~ {.cpp}
///     ./Event 1000 1 1 1
/// ~~~
/// - copytree3
/// Example macro to copy a subset of a tree to a new tree.
/// Only selected entries are copied to the new tree.
/// NOTE that only the active branches are copied.

   virtual TBasket        *CreateBasket(TBranch*);/// Create a basket for this tree and given branch.
   virtual void            DirectoryAutoAdd(TDirectory *);
 /// Called by TKey and TObject::Clone to automatically add us to a directory
 /// when we are read from a file.

   Int_t                   Debug() const { return fDebug; }
   virtual void            Delete(Option_t* option = ""); // *MENU*
/// Delete this tree from memory or/and disk.
/// - if option == "all" delete Tree object from memory AND from disk
///                     all baskets on disk are deleted. All keys with same name
///                     are deleted.
/// - if option =="" only Tree object in memory is deleted.

   virtual void            Draw(Option_t* opt) { Draw(opt, "", "", kMaxEntries, 0); }
   virtual Long64_t        Draw(const char* varexp, const TCut& selection, Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0);
/// Draw expression varexp for specified entries.
/// Returns -1 in case of error or number of selected events in case of success.
/// This function accepts TCut objects as arguments.
/// Useful to use the string operator +
/// Example:
///     ntuple.Draw("x",cut1+cut2+cut3);

   virtual Long64_t        Draw(const char* varexp, const char* selection, Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0); // *MENU*
/// Draw expression varexp for specified entries.
/// Returns -1 in case of error or number of selected events in case of success.
/// varexp is an expression of the general form
///  - "e1"           produces a 1-d histogram (TH1F) of expression "e1"
///  - "e1:e2"        produces an unbinned 2-d scatter-plot (TGraph) of "e1"
///                   on the y-axis versus "e2" on the x-axis
///  - "e1:e2:e3"     produces an unbinned 3-d scatter-plot (TPolyMarker3D) of "e1"
///                   versus "e2" versus "e3" on the x-, y-, z-axis, respectively.
///  - "e1:e2:e3:e4"  produces an unbinned 3-d scatter-plot (TPolyMarker3D) of "e1"
///                   versus "e2" versus "e3" and "e4" mapped on the color number.
/// (to create histograms in the 2, 3, and 4 dimensional case, see section "Saving
/// the result of Draw to an histogram")
/// Example:
///  -  varexp = x     simplest case: draw a 1-Dim distribution of column named x
///  -  varexp = sqrt(x)            : draw distribution of sqrt(x)
///  -  varexp = x*y/z
///  -  varexp = y:sqrt(x) 2-Dim distribution of y versus sqrt(x)
///  -  varexp = px:py:pz:2.5*E  produces a 3-d scatter-plot of px vs py ps pz
///             and the color number of each marker will be 2.5*E.
///             If the color number is negative it is set to 0.
///             If the color number is greater than the current number of colors
///             it is set to the highest color number.The default number of
///             colors is 50. see TStyle::SetPalette for setting a new color palette.
/// Note that the variables e1, e2 or e3 may contain a selection.
/// example, if e1= x*(y<0), the value histogrammed will be x if y<0
/// and will be 0 otherwise.
/// The expressions can use all the operations and build-in functions
/// supported by TFormula (See TFormula::Analyze), including free
/// standing function taking numerical arguments (TMath::Bessel).
/// In addition, you can call member functions taking numerical
/// arguments. For example:
/// ~~~ {.cpp}
///     TMath::BreitWigner(fPx,3,2)
///     event.GetHistogram().GetXaxis().GetXmax()
/// ~~~
/// Note: You can only pass expression that depend on the TTree's data
/// to static functions and you can only call non-static member function
/// with 'fixed' parameters.
/// selection is an expression with a combination of the columns.
/// In a selection all the C++ operators are authorized.
/// The value corresponding to the selection expression is used as a weight
/// to fill the histogram.
/// If the expression includes only boolean operations, the result
/// is 0 or 1. If the result is 0, the histogram is not filled.
/// In general, the expression may be of the form:
/// ~~~ {.cpp}
///     value*(boolean expression)
/// ~~~
/// if boolean expression is true, the histogram is filled with
/// a `weight = value`.
///
/// Examples:
///  -  selection1 = "x<y && sqrt(z)>3.2"
///  -  selection2 = "(x+y)*(sqrt(z)>3.2)"
///
///  -  selection1 returns a weight = 0 or 1
///  -  selection2 returns a weight = x+y if sqrt(z)>3.2
///                returns a weight = 0 otherwise.
///
/// option is the drawing option.
///  - See TH1::Draw for the list of all drawing options.
///  - If option COL is specified when varexp has three fields:
///~~~ {.cpp}
///      tree.Draw("e1:e2:e3","","col");
///~~~
///    a 2D scatter is produced with e1 vs e2, and e3 is mapped on the color
///    table. The colors for e3 are evaluated once in linear scale before
///    painting. Therefore changing the pad to log scale along Z as no effect
///    on the colors.
///  - If option contains the string "goff", no graphics is generated.
///
/// `nentries` is the number of entries to process (default is all)
/// first is the first entry to process (default is 0)
///
/// This function returns the number of selected entries. It returns -1
/// if an error occurs.
///
/// ## Drawing expressions using arrays and array elements
///
/// Let assumes, a leaf fMatrix, on the branch fEvent, which is a 3 by 3 array,
/// or a TClonesArray.
/// In a TTree::Draw expression you can now access fMatrix using the following
/// syntaxes:
///
/// | String passed   | What is used for each entry of the tree
/// |-----------------|--------------------------------------------------------|
/// | `fMatrix`       | the 9 elements of fMatrix |
/// | `fMatrix[][]`   | the 9 elements of fMatrix |
/// | `fMatrix[2][2]` | only the elements fMatrix[2][2] |
/// | `fMatrix[1]`    | the 3 elements fMatrix[1][0], fMatrix[1][1] and fMatrix[1][2] |
/// | `fMatrix[1][]`  | the 3 elements fMatrix[1][0], fMatrix[1][1] and fMatrix[1][2] |
/// | `fMatrix[][0]`  | the 3 elements fMatrix[0][0], fMatrix[1][0] and fMatrix[2][0] |
///
/// "fEvent.fMatrix...." same as "fMatrix..." (unless there is more than one leaf named fMatrix!).
///
/// In summary, if a specific index is not specified for a dimension, TTree::Draw
/// will loop through all the indices along this dimension.  Leaving off the
/// last (right most) dimension of specifying then with the two characters '[]'
/// is equivalent.  For variable size arrays (and TClonesArray) the range
/// of the first dimension is recalculated for each entry of the tree.
/// You can also specify the index as an expression of any other variables from the
/// tree.
///
/// TTree::Draw also now properly handling operations involving 2 or more arrays.
///
/// Let assume a second matrix fResults[5][2], here are a sample of some
/// of the possible combinations, the number of elements they produce and
/// the loop used:
///
/// | expression                       | element(s) | Loop                     |
/// |----------------------------------|------------|--------------------------|
/// | `fMatrix[2][1] - fResults[5][2]` |  one       | no loop |
/// | `fMatrix[2][]  - fResults[5][2]` |  three     | on 2nd dim fMatrix |
/// | `fMatrix[2][]  - fResults[5][]`  |  two       | on both 2nd dimensions |
/// | `fMatrix[][2]  - fResults[][1]`  |  three     | on both 1st dimensions |
/// | `fMatrix[][2]  - fResults[][]`   |  six       | on both 1st and 2nd dimensions of fResults |
/// | `fMatrix[][2]  - fResults[3][]`  |  two       | on 1st dim of fMatrix and 2nd of fResults (at the same time) |
/// | `fMatrix[][]   - fResults[][]`   |  six       | on 1st dim then on  2nd dim |
/// | `fMatrix[][fResult[][]]`         |  30        | on 1st dim of fMatrix then on both dimensions of fResults.  The value if fResults[j][k] is used as the second index of fMatrix.|
///
///
/// In summary, TTree::Draw loops through all unspecified dimensions.  To
/// figure out the range of each loop, we match each unspecified dimension
/// from left to right (ignoring ALL dimensions for which an index has been
/// specified), in the equivalent loop matched dimensions use the same index
/// and are restricted to the smallest range (of only the matched dimensions).
/// When involving variable arrays, the range can of course be different
/// for each entry of the tree.
///
/// So the loop equivalent to "fMatrix[][2] - fResults[3][]" is:
/// ~~~ {.cpp}
///     for (Int_t i0; i < min(3,2); i++) {
///        use the value of (fMatrix[i0][2] - fMatrix[3][i0])
///     }
/// ~~~
/// So the loop equivalent to "fMatrix[][2] - fResults[][]" is:
/// ~~~ {.cpp}
///     for (Int_t i0; i < min(3,5); i++) {
///        for (Int_t i1; i1 < 2; i1++) {
///           use the value of (fMatrix[i0][2] - fMatrix[i0][i1])
///        }
///     }
/// ~~~
/// So the loop equivalent to "fMatrix[][] - fResults[][]" is:
/// ~~~ {.cpp}
///     for (Int_t i0; i < min(3,5); i++) {
///        for (Int_t i1; i1 < min(3,2); i1++) {
///           use the value of (fMatrix[i0][i1] - fMatrix[i0][i1])
///        }
///     }
/// ~~~
/// So the loop equivalent to "fMatrix[][fResults[][]]" is:
/// ~~~ {.cpp}
///     for (Int_t i0; i0 < 3; i0++) {
///        for (Int_t j2; j2 < 5; j2++) {
///           for (Int_t j3; j3 < 2; j3++) {
///              i1 = fResults[j2][j3];
///              use the value of fMatrix[i0][i1]
///        }
///     }
/// ~~~
/// ## Retrieving the result of Draw
///
/// By default the temporary histogram created is called "htemp", but only in
/// the one dimensional Draw("e1") it contains the TTree's data points. For
/// a two dimensional Draw, the data is filled into a TGraph which is named
/// "Graph". They can be retrieved by calling
/// ~~~ {.cpp}
///     TH1F *htemp = (TH1F*)gPad->GetPrimitive("htemp"); // 1D
///     TGraph *graph = (TGraph*)gPad->GetPrimitive("Graph"); // 2D
/// ~~~
/// For a three and four dimensional Draw the TPolyMarker3D is unnamed, and
/// cannot be retrieved.
///
/// gPad always contains a TH1 derived object called "htemp" which allows to
/// access the axes:
/// ~~~ {.cpp}
///     TGraph *graph = (TGraph*)gPad->GetPrimitive("Graph"); // 2D
///     TH2F   *htemp = (TH2F*)gPad->GetPrimitive("htemp"); // empty, but has axes
///     TAxis  *xaxis = htemp->GetXaxis();
/// ~~~
/// ## Saving the result of Draw to an histogram
///
/// If varexp0 contains >>hnew (following the variable(s) name(s),
/// the new histogram created is called hnew and it is kept in the current
/// directory (and also the current pad). This works for all dimensions.
///
/// Example:
/// ~~~ {.cpp}
///     tree.Draw("sqrt(x)>>hsqrt","y>0")
/// ~~~
/// will draw `sqrt(x)` and save the histogram as "hsqrt" in the current
/// directory. To retrieve it do:
/// ~~~ {.cpp}
///     TH1F *hsqrt = (TH1F*)gDirectory->Get("hsqrt");
/// ~~~
/// The binning information is taken from the environment variables
/// ~~~ {.cpp}
///     Hist.Binning.?D.?
/// ~~~
/// In addition, the name of the histogram can be followed by up to 9
/// numbers between '(' and ')', where the numbers describe the
/// following:
///
/// -  1 - bins in x-direction
/// -  2 - lower limit in x-direction
/// -  3 - upper limit in x-direction
/// -  4-6 same for y-direction
/// -  7-9 same for z-direction
///
/// When a new binning is used the new value will become the default.
/// Values can be skipped.
///
/// Example:
/// ~~~ {.cpp}
///     tree.Draw("sqrt(x)>>hsqrt(500,10,20)")
///          // plot sqrt(x) between 10 and 20 using 500 bins
///     tree.Draw("sqrt(x):sin(y)>>hsqrt(100,10,60,50,.1,.5)")
///          // plot sqrt(x) against sin(y)
///          // 100 bins in x-direction; lower limit on x-axis is 10; upper limit is 60
///          //  50 bins in y-direction; lower limit on y-axis is .1; upper limit is .5
/// ~~~
/// By default, the specified histogram is reset.
/// To continue to append data to an existing histogram, use "+" in front
/// of the histogram name.
///
/// A '+' in front of the histogram name is ignored, when the name is followed by
/// binning information as described in the previous paragraph.
/// ~~~ {.cpp}
///     tree.Draw("sqrt(x)>>+hsqrt","y>0")
/// ~~~
/// will not reset `hsqrt`, but will continue filling. This works for 1-D, 2-D
/// and 3-D histograms.
///
/// ## Accessing collection objects
///
/// TTree::Draw default's handling of collections is to assume that any
/// request on a collection pertain to it content.  For example, if fTracks
/// is a collection of Track objects, the following:
/// ~~~ {.cpp}
///     tree->Draw("event.fTracks.fPx");
/// ~~~
/// will plot the value of fPx for each Track objects inside the collection.
/// Also
/// ~~~ {.cpp}
///     tree->Draw("event.fTracks.size()");
/// ~~~
/// would plot the result of the member function Track::size() for each
/// Track object inside the collection.
/// To access information about the collection itself, TTree::Draw support
/// the '@' notation.  If a variable which points to a collection is prefixed
/// or postfixed with '@', the next part of the expression will pertain to
/// the collection object.  For example:
/// ~~~ {.cpp}
///     tree->Draw("event.@fTracks.size()");
/// ~~~
/// will plot the size of the collection referred to by `fTracks` (i.e the number
/// of Track objects).
///
/// ## Drawing 'objects'
///
/// When a class has a member function named AsDouble or AsString, requesting
/// to directly draw the object will imply a call to one of the 2 functions.
/// If both AsDouble and AsString are present, AsDouble will be used.
/// AsString can return either a char*, a std::string or a TString.s
/// For example, the following
/// ~~~ {.cpp}
///     tree->Draw("event.myTTimeStamp");
/// ~~~
/// will draw the same histogram as
/// ~~~ {.cpp}
///     tree->Draw("event.myTTimeStamp.AsDouble()");
/// ~~~
/// In addition, when the object is a type TString or std::string, TTree::Draw
/// will call respectively `TString::Data` and `std::string::c_str()`
///
/// If the object is a TBits, the histogram will contain the index of the bit
/// that are turned on.
///
/// ## Retrieving  information about the tree itself.
///
/// You can refer to the tree (or chain) containing the data by using the
/// string 'This'.
/// You can then could any TTree methods. For example:
/// ~~~ {.cpp}
///     tree->Draw("This->GetReadEntry()");
/// ~~~
/// will display the local entry numbers be read.
/// ~~~ {.cpp}
///     tree->Draw("This->GetUserInfo()->At(0)->GetName()");
/// ~~~
///  will display the name of the first 'user info' object.
///
/// ## Special functions and variables
///
/// `Entry$`:  A TTree::Draw formula can use the special variable `Entry$`
/// to access the entry number being read. For example to draw every
/// other entry use:
/// ~~~ {.cpp}
///     tree.Draw("myvar","Entry$%2==0");
/// ~~~
/// - `Entry$`      : return the current entry number (`== TTree::GetReadEntry()`)
/// - `LocalEntry$` : return the current entry number in the current tree of a
///   chain (`== GetTree()->GetReadEntry()`)
/// - `Entries$`    : return the total number of entries (== TTree::GetEntries())
/// - `Length$`     : return the total number of element of this formula for this
///   entry (`==TTreeFormula::GetNdata()`)
/// - `Iteration$`  : return the current iteration over this formula for this
///   entry (i.e. varies from 0 to `Length$`).
/// - `Length$(formula )`  : return the total number of element of the formula
///   given as a parameter.
/// - `Sum$(formula )`  : return the sum of the value of the elements of the
///   formula given as a parameter.  For example the mean for all the elements in
///   one entry can be calculated with:
///   `Sum$(formula )/Length$(formula )`
/// - `Min$(formula )` : return the minimun (within one TTree entry) of the value of the
///    elements of the formula given as a parameter.
/// - `Max$(formula )` : return the maximum (within one TTree entry) of the value of the
///   elements of the formula given as a parameter.
/// - `MinIf$(formula,condition)`
/// - `MaxIf$(formula,condition)` : return the minimum (maximum) (within one TTree entry)
///   of the value of the elements of the formula given as a parameter
///   if they match the condition. If no element matches the condition,
///   the result is zero.  To avoid the resulting peak at zero, use the
///   pattern:
/// ~~~ {.cpp}
///        tree->Draw("MinIf$(formula,condition)","condition");
/// ~~~
///   which will avoid calculation `MinIf$` for the entries that have no match
///   for the condition.
/// - `Alt$(primary,alternate)` : return the value of "primary" if it is available
///   for the current iteration otherwise return the value of "alternate".
///   For example, with arr1[3] and arr2[2]
/// ~~~ {.cpp}
///        tree->Draw("arr1+Alt$(arr2,0)");
/// ~~~
///   will draw arr1[0]+arr2[0] ; arr1[1]+arr2[1] and arr1[2]+0
///   Or with a variable size array arr3
/// ~~~ {.cpp}
///        tree->Draw("Alt$(arr3[0],0)+Alt$(arr3[1],0)+Alt$(arr3[2],0)");
/// ~~~
///   will draw the sum arr3 for the index 0 to min(2,actual_size_of_arr3-1)
///   As a comparison
/// ~~~ {.cpp}
///        tree->Draw("arr3[0]+arr3[1]+arr3[2]");
/// ~~~
///   will draw the sum arr3 for the index 0 to 2 only if the
///   actual_size_of_arr3 is greater or equal to 3.
///   Note that the array in 'primary' is flattened/linearized thus using
///   Alt$ with multi-dimensional arrays of different dimensions in unlikely
///   to yield the expected results.  To visualize a bit more what elements
///   would be matched by TTree::Draw, TTree::Scan can be used:
/// ~~~ {.cpp}
///        tree->Scan("arr1:Alt$(arr2,0)");
/// ~~~
///   will print on one line the value of arr1 and (arr2,0) that will be
///   matched by
/// ~~~ {.cpp}
///        tree->Draw("arr1-Alt$(arr2,0)");
/// ~~~
/// The ternary operator is not directly supported in TTree::Draw however, to plot the
/// equivalent of `var2<20 ? -99 : var1`, you can use:
/// ~~~ {.cpp}
///     tree->Draw("(var2<20)*99+(var2>=20)*var1","");
/// ~~~
/// ## Drawing a user function accessing the TTree data directly
///
/// If the formula contains  a file name, TTree::MakeProxy will be used
/// to load and execute this file.   In particular it will draw the
/// result of a function with the same name as the file.  The function
/// will be executed in a context where the name of the branches can
/// be used as a C++ variable.
///
/// For example draw px using the file hsimple.root (generated by the
/// hsimple.C tutorial), we need a file named hsimple.cxx:
/// ~~~ {.cpp}
///     double hsimple() {
///        return px;
///     }
/// ~~~
/// MakeProxy can then be used indirectly via the TTree::Draw interface
/// as follow:
/// ~~~ {.cpp}
///     new TFile("hsimple.root")
///     ntuple->Draw("hsimple.cxx");
/// ~~~
/// A more complete example is available in the tutorials directory:
/// `h1analysisProxy.cxx`, `h1analysProxy.h` and `h1analysisProxyCut.C`
/// which reimplement the selector found in `h1analysis.C`
///
/// The main features of this facility are:
///
///  * on-demand loading of branches
///  * ability to use the 'branchname' as if it was a data member
///  * protection against array out-of-bound
///  * ability to use the branch data as object (when the user code is available)
///
///  See TTree::MakeProxy for more details.
///
/// ## Making a Profile histogram
///
///  In case of a 2-Dim expression, one can generate a TProfile histogram
///  instead of a TH2F histogram by specifying option=prof or option=profs
///  or option=profi or option=profg ; the trailing letter select the way
///  the bin error are computed, See TProfile2D::SetErrorOption for
///  details on the differences.
///  The option=prof is automatically selected in case of y:x>>pf
///  where pf is an existing TProfile histogram.
///
/// ## Making a 2D Profile histogram
///
/// In case of a 3-Dim expression, one can generate a TProfile2D histogram
/// instead of a TH3F histogram by specifying option=prof or option=profs.
/// or option=profi or option=profg ; the trailing letter select the way
/// the bin error are computed, See TProfile2D::SetErrorOption for
/// details on the differences.
/// The option=prof is automatically selected in case of z:y:x>>pf
/// where pf is an existing TProfile2D histogram.
///
/// ## Making a 5D plot using GL
///
/// If option GL5D is specified together with 5 variables, a 5D plot is drawn
/// using OpenGL. See $ROOTSYS/tutorials/tree/staff.C as example.
///
/// ## Making a parallel coordinates plot
///
/// In case of a 2-Dim or more expression with the option=para, one can generate
/// a parallel coordinates plot. With that option, the number of dimensions is
/// arbitrary. Giving more than 4 variables without the option=para or
/// option=candle or option=goff will produce an error.
///
/// ## Making a candle sticks chart
///
/// In case of a 2-Dim or more expression with the option=candle, one can generate
/// a candle sticks chart. With that option, the number of dimensions is
/// arbitrary. Giving more than 4 variables without the option=para or
/// option=candle or option=goff will produce an error.
///
/// ## Normalizing the output histogram to 1
///
/// When option contains "norm" the output histogram is normalized to 1.
///
/// ## Saving the result of Draw to a TEventList, a TEntryList or a TEntryListArray
///
/// TTree::Draw can be used to fill a TEventList object (list of entry numbers)
/// instead of histogramming one variable.
/// If varexp0 has the form >>elist , a TEventList object named "elist"
/// is created in the current directory. elist will contain the list
/// of entry numbers satisfying the current selection.
/// If option "entrylist" is used, a TEntryList object is created
/// If the selection contains arrays, vectors or any container class and option
/// "entrylistarray" is used, a TEntryListArray object is created
/// containing also the subentries satisfying the selection, i.e. the indices of
/// the branches which hold containers classes.
/// Example:
/// ~~~ {.cpp}
///     tree.Draw(">>yplus","y>0")
/// ~~~
/// will create a TEventList object named "yplus" in the current directory.
/// In an interactive session, one can type (after TTree::Draw)
/// ~~~ {.cpp}
///     yplus.Print("all")
/// ~~~
/// to print the list of entry numbers in the list.
/// ~~~ {.cpp}
///     tree.Draw(">>yplus", "y>0", "entrylist")
/// ~~~
/// will create a TEntryList object names "yplus" in the current directory
/// ~~~ {.cpp}
///     tree.Draw(">>yplus", "y>0", "entrylistarray")
/// ~~~
/// will create a TEntryListArray object names "yplus" in the current directory
///
/// By default, the specified entry list is reset.
/// To continue to append data to an existing list, use "+" in front
/// of the list name;
/// ~~~ {.cpp}
///     tree.Draw(">>+yplus","y>0")
/// ~~~
/// will not reset yplus, but will enter the selected entries at the end
/// of the existing list.
///
/// ## Using a TEventList, TEntryList or TEntryListArray as Input
///
/// Once a TEventList or a TEntryList object has been generated, it can be used as input
/// for TTree::Draw. Use TTree::SetEventList or TTree::SetEntryList to set the
/// current event list
///
/// Example 1:
/// ~~~ {.cpp}
///     TEventList *elist = (TEventList*)gDirectory->Get("yplus");
///     tree->SetEventList(elist);
///     tree->Draw("py");
/// ~~~
/// Example 2:
/// ~~~ {.cpp}
///     TEntryList *elist = (TEntryList*)gDirectory->Get("yplus");
///     tree->SetEntryList(elist);
///     tree->Draw("py");
/// ~~~
/// If a TEventList object is used as input, a new TEntryList object is created
/// inside the SetEventList function. In case of a TChain, all tree headers are loaded
/// for this transformation. This new object is owned by the chain and is deleted
/// with it, unless the user extracts it by calling GetEntryList() function.
/// See also comments to SetEventList() function of TTree and TChain.
///
/// If arrays are used in the selection criteria and TEntryListArray is not used,
/// all the entries that have at least one element of the array that satisfy the selection
/// are entered in the list.
///
/// Example:
/// ~~~ {.cpp}
///     tree.Draw(">>pyplus","fTracks.fPy>0");
///     tree->SetEventList(pyplus);
///     tree->Draw("fTracks.fPy");
/// ~~~
///  will draw the fPy of ALL tracks in event with at least one track with
///  a positive fPy.
///
/// To select only the elements that did match the original selection
/// use TEventList::SetReapplyCut or TEntryList::SetReapplyCut.
///
/// Example:
/// ~~~ {.cpp}
///     tree.Draw(">>pyplus","fTracks.fPy>0");
///     pyplus->SetReapplyCut(kTRUE);
///     tree->SetEventList(pyplus);
///     tree->Draw("fTracks.fPy");
/// ~~~
/// will draw the fPy of only the tracks that have a positive fPy.
///
/// To draw only the elements that match a selection in case of arrays,
/// you can also use TEntryListArray (faster in case of a more general selection).
///
/// Example:
/// ~~~ {.cpp}
///     tree.Draw(">>pyplus","fTracks.fPy>0", "entrylistarray");
///     tree->SetEntryList(pyplus);
///     tree->Draw("fTracks.fPy");
/// ~~~
/// will draw the fPy of only the tracks that have a positive fPy,
/// but without redoing the selection.
///
///  Note: Use tree->SetEventList(0) if you do not want use the list as input.
///
/// ## How to obtain more info from TTree::Draw
///
///  Once TTree::Draw has been called, it is possible to access useful
///  information still stored in the TTree object via the following functions:
///
/// - GetSelectedRows() // return the number of values accepted by the selection expression. In case where no selection was specified, returns the number of values processed.
/// - GetV1()           // returns a pointer to the double array of V1
/// - GetV2()           // returns a pointer to the double array of V2
/// - GetV3()           // returns a pointer to the double array of V3
/// - GetV4()           // returns a pointer to the double array of V4
/// - GetW()            // returns a pointer to the double array of Weights where weight equal the result of the selection expression.
///
/// where V1,V2,V3 correspond to the expressions in
/// ~~~ {.cpp}
///     TTree::Draw("V1:V2:V3:V4",selection);
/// ~~~
/// If the expression has more than 4 component use GetVal(index)
///
/// Example:
/// ~~~ {.cpp}
///     Root > ntuple->Draw("py:px","pz>4");
///     Root > TGraph *gr = new TGraph(ntuple->GetSelectedRows(),
///                                   ntuple->GetV2(), ntuple->GetV1());
///     Root > gr->Draw("ap"); //draw graph in current pad
/// ~~~
/// creates a TGraph object with a number of points corresponding to the
/// number of entries selected by the expression "pz>4", the x points of the graph
/// being the px values of the Tree and the y points the py values.
///
/// Important note: By default TTree::Draw creates the arrays obtained
/// with GetW, GetV1, GetV2, GetV3, GetV4, GetVal with a length corresponding
/// to the parameter fEstimate.  The content will be the last `GetSelectedRows() % GetEstimate()`
/// values calculated.
/// By default fEstimate=1000000 and can be modified
/// via TTree::SetEstimate. To keep in memory all the results (in case
/// where there is only one result per entry), use
/// ~~~ {.cpp}
///     tree->SetEstimate(tree->GetEntries()+1); // same as tree->SetEstimate(-1);
/// ~~~
/// You must call SetEstimate if the expected number of selected rows
/// you need to look at is greater than 1000000.
///
/// You can use the option "goff" to turn off the graphics output
/// of TTree::Draw in the above example.
///
/// ## Automatic interface to TTree::Draw via the TTreeViewer
/// A complete graphical interface to this function is implemented
/// in the class TTreeViewer.
/// To start the TTreeViewer, three possibilities:
/// - select TTree context menu item "StartViewer"
/// - type the command  "TTreeViewer TV(treeName)"
/// - execute statement "tree->StartViewer();"

   virtual void            DropBaskets();/// Remove some baskets from memory.
   virtual void            DropBuffers(Int_t nbytes);/// Drop branch buffers to accommodate nbytes below MaxVirtualsize.
   virtual Int_t           Fill();//填充到buffer中,一定数量之后写入硬盘
/// Fill all branches.
/// This function loops on all the branches of this tree.  For
/// each branch, it copies to the branch buffer (basket) the current
/// values of the leaves data types. If a leaf is a simple data type,
/// a simple conversion to a machine independent format has to be done.
/// This machine independent version of the data is copied into a
/// basket (each branch has its own basket).  When a basket is full
/// (32k worth of data by default), it is then optionally compressed
/// and written to disk (this operation is also called committing or
/// 'flushing' the basket).  The committed baskets are then
/// immediately removed from memory.
/// The function returns the number of bytes committed to the
/// individual branches.
/// If a write error occurs, the number of bytes returned is -1.
/// If no data are written, because, e.g., the branch is disabled,
/// the number of bytes returned is 0.
/// __The baskets are flushed and the Tree header saved at regular intervals__
/// At regular intervals, when the amount of data written so far is
/// greater than fAutoFlush (see SetAutoFlush) all the baskets are flushed to disk.
/// This makes future reading faster as it guarantees that baskets belonging to nearby
/// entries will be on the same disk region.
/// When the first call to flush the baskets happen, we also take this opportunity
/// to optimize the baskets buffers.
/// We also check if the amount of data written is greater than fAutoSave (see SetAutoSave).
/// In this case we also write the Tree header. This makes the Tree recoverable up to this point
/// in case the program writing the Tree crashes.
/// The decisions to FlushBaskets and Auto Save can be made based either on the number
/// of bytes written (fAutoFlush and fAutoSave negative) or on the number of entries
/// written (fAutoFlush and fAutoSave positive).
/// Note that the user can decide to call FlushBaskets and AutoSave in her event loop
/// base on the number of events written instead of the number of bytes written.
/// Note that calling FlushBaskets too often increases the IO time.
/// Note that calling AutoSave too often increases the IO time and also the file size.

   virtual TBranch        *FindBranch(const char* name);
/// Return the branch that correspond to the path 'branchname', which can
/// include the name of the tree or the omitted name of the parent branches.
/// In case of ambiguity, returns the first match.

   virtual TLeaf          *FindLeaf(const char* name);/// Find leaf..
   virtual Int_t           Fit(const char* funcname, const char* varexp, const char* selection = "", Option_t* option = "", Option_t* goption = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0); // *MENU*
/// Fit  a projected item(s) from a tree.
/// funcname is a TF1 function.
/// See TTree::Draw() for explanations of the other parameters.
/// By default the temporary histogram created is called htemp.
/// If varexp contains >>hnew , the new histogram created is called hnew
/// and it is kept in the current directory.
/// The function returns the number of selected entries.
/// ## Return status
///  The function returns the status of the histogram fit (see TH1::Fit)
///  If no entries were selected, the function returns -1;
///   (i.e. fitResult is null is the fit is OK)

   virtual Int_t           FlushBaskets() const;
/// Write to disk all the basket that have not yet been individually written.
/// Return the number of bytes written or -1 in case of write error.

   virtual const char     *GetAlias(const char* aliasName) const;/// Returns the expanded value of the alias.  Search in the friends if any.
   virtual Long64_t        GetAutoFlush() const {return fAutoFlush;}
   virtual Long64_t        GetAutoSave()  const {return fAutoSave;}
   virtual TBranch        *GetBranch(const char* name);/// Return pointer to the branch with the given name in this tree or its friends.
   virtual TBranchRef     *GetBranchRef() const { return fBranchRef; };
   virtual Bool_t          GetBranchStatus(const char* branchname) const;
/// Return status of branch with name branchname.
/// - 0 if branch is not activated
/// - 1 if branch is activated

   static  Int_t           GetBranchStyle();
/// Static function returning the current branch style.
/// - style = 0 old Branch
/// - style = 1 new Bronch

   virtual Long64_t        GetCacheSize() const { return fCacheSize; }
   virtual TClusterIterator GetClusterIterator(Long64_t firstentry);
/// Return an iterator over the cluster of baskets starting at firstentry.
/// This iterator is not yet supported for TChain object.

   virtual Long64_t        GetChainEntryNumber(Long64_t entry) const { return entry; }
   virtual Long64_t        GetChainOffset() const { return fChainOffset; }
   TFile                  *GetCurrentFile() const;/// Return pointer to the current file.
           Int_t           GetDefaultEntryOffsetLen() const {return fDefaultEntryOffsetLen;}
           Long64_t        GetDebugMax()  const { return fDebugMax; }
           Long64_t        GetDebugMin()  const { return fDebugMin; }
   TDirectory             *GetDirectory() const { return fDirectory; }
   virtual Long64_t        GetEntries() const   { return fEntries; }//获取entry数
   virtual Long64_t        GetEntries(const char *selection);
/// Return the number of entries matching the selection.
/// Return -1 in case of errors.
/// If the selection uses any arrays or containers, we return the number
/// of entries where at least one element match the selection.
/// GetEntries is implemented using the selector class TSelectorEntries,
/// which can be used directly (see code in TTreePlayer::GetEntries) for
/// additional option.
/// If SetEventList was used on the TTree or TChain, only that subset
/// of entries will be considered.

   virtual Long64_t        GetEntriesFast() const   { return fEntries; }
   virtual Long64_t        GetEntriesFriend() const;
/// Return pointer to the 1st Leaf named name in any Branch of this Tree or
/// any branch in the list of friend trees.

   virtual Long64_t        GetEstimate() const { return fEstimate; }
   virtual Int_t           GetEntry(Long64_t entry = 0, Int_t getall = 0);
/// Read all branches of entry and return total number of bytes read.
/// - getall = 0 : get only active branches
/// - getall = 1 : get all branches
/// The function returns the number of bytes read from the input buffer.
/// If entry does not exist the function returns 0.
/// If an I/O error occurs, the function returns -1.
/// If the Tree has friends, also read the friends entry.
/// ## IMPORTANT NOTE
///
/// By default, GetEntry reuses the space allocated by the previous object
/// for each branch. You can force the previous object to be automatically
/// deleted if you call mybranch.SetAutoDelete(kTRUE) (default is kFALSE).

           Int_t           GetEvent(Long64_t entry = 0, Int_t getall = 0) { return GetEntry(entry, getall); }
   virtual Int_t           GetEntryWithIndex(Int_t major, Int_t minor = 0);
/// Read entry corresponding to major and minor number.
///  The function returns the total number of bytes read.
///  If the Tree has friend trees, the corresponding entry with
///  the index values (major,minor) is read. Note that the master Tree
///  and its friend may have different entry serial numbers corresponding
///  to (major,minor).

   virtual Long64_t        GetEntryNumberWithBestIndex(Long64_t major, Long64_t minor = 0) const;
/// Return entry number corresponding to major and minor number.
/// Note that this function returns only the entry number, not the data
/// To read the data corresponding to an entry number, use TTree::GetEntryWithIndex
/// the BuildIndex function has created a table of Long64_t* of sorted values
/// corresponding to val = major<<31 + minor;
/// The function performs binary search in this sorted table.
/// If it finds a pair that matches val, it returns directly the
/// index in the table.
/// If an entry corresponding to major and minor is not found, the function
/// returns the index of the major,minor pair immediately lower than the
/// requested value, ie it will return -1 if the pair is lower than
/// the first entry in the index.
/// See also GetEntryNumberWithIndex

   virtual Long64_t        GetEntryNumberWithIndex(Long64_t major, Long64_t minor = 0) const;
/// Return entry number corresponding to major and minor number.
/// Note that this function returns only the entry number, not the data
/// To read the data corresponding to an entry number, use TTree::GetEntryWithIndex
/// the BuildIndex function has created a table of Long64_t* of sorted values
/// corresponding to val = major<<31 + minor;
/// The function performs binary search in this sorted table.
/// If it finds a pair that matches val, it returns directly the
/// index in the table, otherwise it returns -1.
/// See also GetEntryNumberWithBestIndex

   TEventList             *GetEventList() const { return fEventList; }
   virtual TEntryList     *GetEntryList();///Returns the entry list, set to this tree
   virtual Long64_t        GetEntryNumber(Long64_t entry) const;
/// Return entry number corresponding to entry.
/// if no TEntryList set returns entry
/// else returns the entry number corresponding to the list index=entry

   virtual Int_t           GetFileNumber() const { return fFileNumber; }
   virtual TTree          *GetFriend(const char*) const;/// Return a pointer to the TTree friend whose name or alias is 'friendname.
   virtual const char     *GetFriendAlias(TTree*) const;
/// If the 'tree' is a friend, this method returns its alias name.
/// This alias is an alternate name for the tree.
/// It can be used in conjunction with a branch or leaf name in a TTreeFormula,
/// to specify in which particular tree the branch or leaf can be found if
/// the friend trees have branches or leaves with the same name as the master
/// tree.
/// It can also be used in conjunction with an alias created using
/// TTree::SetAlias in a TTreeFormula, e.g.:
///      maintree->Draw("treealias.fPx - treealias.myAlias");
/// where fPx is a branch of the friend tree aliased as 'treealias' and 'myAlias'
/// was created using TTree::SetAlias on the friend tree.
/// However, note that 'treealias.myAlias' will be expanded literally,
/// without remembering that it comes from the aliased friend and thus
/// the branch name might not be disambiguated properly, which means
/// that you may not be able to take advantage of this feature.

   TH1                    *GetHistogram() { return GetPlayer()->GetHistogram(); }
   virtual Int_t          *GetIndex() { return &fIndex.fArray[0]; }
   virtual Double_t       *GetIndexValues() { return &fIndexValues.fArray[0]; }
   virtual TIterator      *GetIteratorOnAllLeaves(Bool_t dir = kIterForward);
/// Creates a new iterator that will go through all the leaves on the tree itself and its friend.

   virtual TLeaf          *GetLeaf(const char* branchname, const char* leafname);
/// Return pointer to the 1st Leaf named name in any Branch of this
/// Tree or any branch in the list of friend trees.
/// The leaf name can contain the name of a friend tree with the
/// syntax: friend_dir_and_tree.full_leaf_name
/// the friend_dir_and_tree can be of the form:
///     TDirectoryName/TreeName

   virtual TLeaf          *GetLeaf(const char* name);
/// Return pointer to the 1st Leaf named name in any Branch of this
/// Tree or any branch in the list of friend trees.
/// aname may be of the form branchname/leafname

   virtual TList          *GetListOfClones() { return fClones; }
   virtual TObjArray      *GetListOfBranches() { return &fBranches; }
   virtual TObjArray      *GetListOfLeaves() { return &fLeaves; }
   virtual TList          *GetListOfFriends() const { return fFriends; }
   virtual TList          *GetListOfAliases() const { return fAliases; }

   // GetMakeClass is left non-virtual for efficiency reason.
   // Making it virtual affects the performance of the I/O
           Int_t           GetMakeClass() const { return fMakeClass; }

   virtual Long64_t        GetMaxEntryLoop() const { return fMaxEntryLoop; }
   virtual Double_t        GetMaximum(const char* columname);
/// Return maximum of column with name columname.
/// if the Tree has an associated TEventList or TEntryList, the maximum
/// is computed for the entries in this list.

   static  Long64_t        GetMaxTreeSize();/// Static function which returns the tree file size limit in bytes.
   virtual Long64_t        GetMaxVirtualSize() const { return fMaxVirtualSize; }
   virtual Double_t        GetMinimum(const char* columname);
/// Return minimum of column with name columname.
/// if the Tree has an associated TEventList or TEntryList, the minimum
/// is computed for the entries in this list.

   virtual Int_t           GetNbranches() { return fBranches.GetEntriesFast(); }
   TObject                *GetNotify() const { return fNotify; }
   TVirtualTreePlayer     *GetPlayer();/// Load the TTreePlayer (if not already done).
   virtual Int_t           GetPacketSize() const { return fPacketSize; }
   virtual TVirtualPerfStats *GetPerfStats() const { return fPerfStats; }
   virtual Long64_t        GetReadEntry()  const { return fReadEntry; }
   virtual Long64_t        GetReadEvent()  const { return fReadEntry; }
   virtual Int_t           GetScanField()  const { return fScanField; }
   TTreeFormula           *GetSelect()    { return GetPlayer()->GetSelect(); }
   virtual Long64_t        GetSelectedRows() { return GetPlayer()->GetSelectedRows(); }
   virtual Int_t           GetTimerInterval() const { return fTimerInterval; }
           TBuffer*        GetTransientBuffer(Int_t size);
/// Returns the transient buffer currently used by this TTree for reading/writing baskets.

   virtual Long64_t        GetTotBytes() const { return fTotBytes; }
   virtual TTree          *GetTree() const { return const_cast<TTree*>(this); }
   virtual TVirtualIndex  *GetTreeIndex() const { return fTreeIndex; }
   virtual Int_t           GetTreeNumber() const { return 0; }
   virtual Int_t           GetUpdate() const { return fUpdate; }
   virtual TList          *GetUserInfo();
/// Return a pointer to the list containing user objects associated to this tree.
/// The list is automatically created if it does not exist.
/// WARNING: By default the TTree destructor will delete all objects added
/// to this list. If you do not want these objects to be deleted,
/// call:
///     mytree->GetUserInfo()->Clear();
/// before deleting the tree.

   // See TSelectorDraw::GetVar
   TTreeFormula           *GetVar(Int_t i)  { return GetPlayer()->GetVar(i); }
   // See TSelectorDraw::GetVar
   TTreeFormula           *GetVar1() { return GetPlayer()->GetVar1(); }
   // See TSelectorDraw::GetVar
   TTreeFormula           *GetVar2() { return GetPlayer()->GetVar2(); }
   // See TSelectorDraw::GetVar
   TTreeFormula           *GetVar3() { return GetPlayer()->GetVar3(); }
   // See TSelectorDraw::GetVar
   TTreeFormula           *GetVar4() { return GetPlayer()->GetVar4(); }
   // See TSelectorDraw::GetVal
   virtual Double_t       *GetVal(Int_t i)   { return GetPlayer()->GetVal(i); }
   // See TSelectorDraw::GetVal
   virtual Double_t       *GetV1()   { return GetPlayer()->GetV1(); }
   // See TSelectorDraw::GetVal
   virtual Double_t       *GetV2()   { return GetPlayer()->GetV2(); }
   // See TSelectorDraw::GetVal
   virtual Double_t       *GetV3()   { return GetPlayer()->GetV3(); }
   // See TSelectorDraw::GetVal
   virtual Double_t       *GetV4()   { return GetPlayer()->GetV4(); }
   virtual Double_t       *GetW()    { return GetPlayer()->GetW(); }
   virtual Double_t        GetWeight() const   { return fWeight; }
   virtual Long64_t        GetZipBytes() const { return fZipBytes; }
   virtual void            IncrementTotalBuffers(Int_t nbytes) { fTotalBuffers += nbytes; }
   Bool_t                  IsFolder() const { return kTRUE; }
   virtual Int_t           LoadBaskets(Long64_t maxmemory = 2000000000);
/// Read in memory all baskets from all branches up to the limit of maxmemory bytes.
/// If maxmemory is non null and positive SetMaxVirtualSize is called
/// with this value. Default for maxmemory is 2000000000 (2 Gigabytes).
/// The function returns the total number of baskets read into memory
/// if negative an error occurred while loading the branches.
/// This method may be called to force branch baskets in memory
/// when random access to branch entries is required.
/// If random access to only a few branches is required, you should
/// call directly TBranch::LoadBaskets.

   virtual Long64_t        LoadTree(Long64_t entry);
/// Set current entry.
/// Returns -2 if entry does not exist (just as TChain::LoadTree()).
/// Note: This function is overloaded in TChain.

   virtual Long64_t        LoadTreeFriend(Long64_t entry, TTree* T);
/// Load entry on behalf of our master tree, we may use an index.
/// Called by LoadTree() when the masterTree looks for the entry
/// number in a friend tree (us) corresponding to the passed entry
/// number in the masterTree.
/// If we have no index, our entry number and the masterTree entry
/// number are the same.
/// If we *do* have an index, we must find the (major, minor) value pair
/// in masterTree to locate our corresponding entry.

   virtual Int_t           MakeClass(const char* classname = 0, Option_t* option = "");
/// Generate a skeleton analysis class for this tree.
/// The following files are produced: classname.h and classname.C.
/// If classname is 0, classname will be called "nameoftree".
/// The generated code in classname.h includes the following:
/// - Identification of the original tree and the input file name.
/// - Definition of an analysis class (data members and member functions).
/// - The following member functions:
///   - constructor (by default opening the tree file),
///   - GetEntry(Long64_t entry),
///   - Init(TTree* tree) to initialize a new TTree,
///   - Show(Long64_t entry) to read and dump entry.
/// The generated code in classname.C includes only the main
/// analysis function Loop.
/// NOTE: Do not use the code generated for a single TTree which is part
/// of a TChain to process that entire TChain.  The maximum dimensions
/// calculated for arrays on the basis of a single TTree from the TChain
/// might be (will be!) too small when processing all of the TTrees in
/// the TChain.  You must use myChain.MakeClass() to generate the code,
/// not myTree.MakeClass(...).

   virtual Int_t           MakeCode(const char* filename = 0);
/// Generate a skeleton function for this tree.
/// The function code is written on filename.
/// If filename is 0, filename will be called nameoftree.C
/// The generated code includes the following:
/// - Identification of the original Tree and Input file name,
/// - Opening the Tree file,
/// - Declaration of Tree variables,
/// - Setting of branches addresses,
/// - A skeleton for the entry loop.
/// To use this function:
/// - Open your Tree file (eg: TFile f("myfile.root");)
/// - T->MakeCode("MyAnalysis.C");
/// where T is the name of the TTree in file myfile.root
/// and MyAnalysis.C the name of the file created by this function.
/// NOTE: Since the implementation of this function, a new and better
/// function TTree::MakeClass() has been developed.

   virtual Int_t           MakeProxy(const char* classname, const char* macrofilename = 0, const char* cutfilename = 0, const char* option = 0, Int_t maxUnrolling = 3);
/// Generate a skeleton analysis class for this Tree using TBranchProxy.
/// TBranchProxy is the base of a class hierarchy implementing an
/// indirect access to the content of the branches of a TTree.
/// "proxyClassname" is expected to be of the form:
///     [path/]fileprefix
/// The skeleton will then be generated in the file:
///     fileprefix.h
/// located in the current directory or in 'path/' if it is specified.
/// The class generated will be named 'fileprefix'
///
/// "macrofilename" and optionally "cutfilename" are expected to point
/// to source files which will be included by the generated skeleton.
/// Method of the same name as the file(minus the extension and path)
/// will be called by the generated skeleton's Process method as follow:
///     [if (cutfilename())] htemp->Fill(macrofilename());
/// "option" can be used select some of the optional features during
/// the code generation.  The possible options are:
/// - nohist : indicates that the generated ProcessFill should not fill the histogram.
/// 'maxUnrolling' controls how deep in the class hierarchy does the
/// system 'unroll' classes that are not split.  Unrolling a class
/// allows direct access to its data members (this emulates the behavior
/// of TTreeFormula).
///
/// The main features of this skeleton are:
/// * on-demand loading of branches
/// * ability to use the 'branchname' as if it was a data member
/// * protection against array out-of-bounds errors
/// * ability to use the branch data as an object (when the user code is available)
/// If a file name macrofilename.h (or .hh, .hpp, .hxx, .hPP, .hXX) exist
/// it is included before the declaration of the proxy class.  This can
/// be used in particular to insure that the include files needed by
/// the macro file are properly loaded.
/// The default histogram is accessible via the variable named 'htemp'.
/// If the library of the classes describing the data in the branch is
/// loaded, the skeleton will add the needed #include statements and
/// give the ability to access the object stored in the branches.

   virtual Int_t           MakeSelector(const char* selector = 0, Option_t* option = "");//生成要Process()的文件
/// Generate skeleton selector class for this tree.
/// The following files are produced: selector.h and selector.C.
/// If selector is 0, the selector will be called "nameoftree".
/// The option can be used to specify the branches that will have a data member.
///    - If option is "=legacy", a pre-ROOT6 selector will be generated (data
///      members and branch pointers instead of TTreeReaders).
///    - If option is empty, readers will be generated for each leaf.
///    - If option is "@", readers will be generated for the topmost branches.
///    - Individual branches can also be picked by their name:
///       - "X" generates readers for leaves of X.
///       - "@X" generates a reader for X as a whole.
///       - "@X;Y" generates a reader for X as a whole and also readers for the
///         leaves of Y.
///    - For further examples see the figure below.
/// The generated code in selector.h includes the following:
///    - Identification of the original Tree and Input file name
///    - Definition of selector class (data and functions)
///    - The following class functions:
///       - constructor and destructor
///       - void    Begin(TTree *tree)
///       - void    SlaveBegin(TTree *tree)
///       - void    Init(TTree *tree)
///       - Bool_t  Notify()
///       - Bool_t  Process(Long64_t entry)
///       - void    Terminate()
///       - void    SlaveTerminate()
/// The class selector derives from TSelector.
/// The generated code in selector.C includes empty functions defined above.
/// To use this function:
///    - connect your Tree file (eg: `TFile f("myfile.root");`)
///    - `T->MakeSelector("myselect");`
/// where T is the name of the Tree in file myfile.root
/// and myselect.h, myselect.C the name of the files created by this function.
/// In a ROOT session, you can do:
///     root > T->Process("myselect.C")

   Bool_t                  MemoryFull(Int_t nbytes);/// Check if adding nbytes to memory we are still below MaxVirtualsize.
   virtual Long64_t        Merge(TCollection* list, Option_t* option = "");
/// Merge the trees in the TList into this tree.
/// Returns the total number of entries in the merged tree.

   virtual Long64_t        Merge(TCollection* list, TFileMergeInfo *info);
/// Merge the trees in the TList into this tree.
/// If info->fIsFirst is true, first we clone this TTree info the directory
/// info->fOutputDirectory and then overlay the new TTree information onto
/// this TTree object (so that this TTree object is now the appropriate to
/// use for further merging).
/// Returns the total number of entries in the merged tree.

   static  TTree          *MergeTrees(TList* list, Option_t* option = "");
/// Static function merging the trees in the TList into a new tree.
/// Trees in the list can be memory or disk-resident trees.
/// The new tree is created in the current directory (memory if gROOT).

   virtual Bool_t          Notify();/// Function called when loading a new class library.
   virtual void            OptimizeBaskets(ULong64_t maxMemory=10000000, Float_t minComp=1.1, Option_t *option="");
/// This function may be called after having filled some entries in a Tree
/// Using the information in the existing branch buffers, it will reassign
/// new branch buffer sizes to optimize time and memory.
/// The function computes the best values for branch buffer sizes such that
/// the total buffer sizes is less than maxMemory and nearby entries written
/// at the same time.
/// In case the branch compression factor for the data written so far is less
/// than compMin, the compression is disabled.
/// if option ="d" an analysis report is printed.

   TPrincipal             *Principal(const char* varexp = "", const char* selection = "", Option_t* option = "np", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0);
/// Interface to the Principal Components Analysis class.
/// Create an instance of TPrincipal
/// Fill it with the selected variables
/// - if option "n" is specified, the TPrincipal object is filled with
///                 normalized variables.
/// - If option "p" is specified, compute the principal components
/// - If option "p" and "d" print results of analysis
/// - If option "p" and "h" generate standard histograms
/// - If option "p" and "c" generate code of conversion functions
/// - return a pointer to the TPrincipal object. It is the user responsibility
/// - to delete this object.
/// - The option default value is "np"
/// see TTree::Draw for explanation of the other parameters.
/// The created object is  named "principal" and a reference to it
/// is added to the list of specials Root objects.

   virtual void            Print(Option_t* option = "") const; // *MENU*
/// Print a summary of the tree contents.
/// -  If option contains "all" friend trees are also printed.
/// -  If option contains "toponly" only the top level branches are printed.
/// -  If option contains "clusters" information about the cluster of baskets is printed.
/// Wildcarding can be used to print only a subset of the branches, e.g.,
/// T.Print("Elec*") will print all branches with name starting with "Elec".

   virtual void            PrintCacheStats(Option_t* option = "") const;
/// print statistics about the TreeCache for this tree, like
/// if option = "a" the list of blocks in the cache is printed

   virtual Long64_t        Process(const char* filename, Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0); // *MENU*
/// Process this tree executing the TSelector code in the specified filename.
/// The return value is -1 in case of error and TSelector::GetStatus() in
/// in case of success.
/// The code in filename is loaded (interpreted or compiled, see below),
/// filename must contain a valid class implementation derived from TSelector,
/// where TSelector has the following member functions:
/// - `Begin()`:         called every time a loop on the tree starts,
///                      a convenient place to create your histograms.
/// - `SlaveBegin()`:    called after Begin(), when on PROOF called only on the
///                      slave servers.
/// - `Process()`:       called for each event, in this function you decide what
///                      to read and fill your histograms.
/// - `SlaveTerminate`:  called at the end of the loop on the tree, when on PROOF
///                      called only on the slave servers.
/// - `Terminate()`:     called at the end of the loop on the tree,
///                      a convenient place to draw/fit your histograms.
/// If filename is of the form file.C, the file will be interpreted.
/// If filename is of the form file.C++, the file file.C will be compiled
/// and dynamically loaded.
/// If filename is of the form file.C+, the file file.C will be compiled
/// and dynamically loaded. At next call, if file.C is older than file.o
/// and file.so, the file.C is not compiled, only file.so is loaded.

#if defined(__CINT__)
#if defined(R__MANUAL_DICT)
   virtual Long64_t        Process(void* selector, Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0);
#endif
#else
   virtual Long64_t        Process(TSelector* selector, Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0);
/// Process this tree executing the code in the specified selector.
/// The return value is -1 in case of error and TSelector::GetStatus() in
/// in case of success.
///   The TSelector class has the following member functions:
/// - `Begin()`:        called every time a loop on the tree starts,
///                     a convenient place to create your histograms.
/// - `SlaveBegin()`:   called after Begin(), when on PROOF called only on the
///                     slave servers.
/// - `Process()`:      called for each event, in this function you decide what
///                     to read and fill your histograms.
/// - `SlaveTerminate`: called at the end of the loop on the tree, when on PROOF
///                     called only on the slave servers.
/// - `Terminate()`:    called at the end of the loop on the tree,
///                     a convenient place to draw/fit your histograms.
///  If the Tree (Chain) has an associated EventList, the loop is on the nentries
///  of the EventList, starting at firstentry, otherwise the loop is on the
///  specified Tree entries.
#endif
   virtual Long64_t        Project(const char* hname, const char* varexp, const char* selection = "", Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0);
/// Make a projection of a tree using selections.
/// Depending on the value of varexp (described in Draw) a 1-D, 2-D, etc.,
/// projection of the tree will be filled in histogram hname.
/// Note that the dimension of hname must match with the dimension of varexp.

   virtual TSQLResult     *Query(const char* varexp = "", const char* selection = "", Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0);/// Loop over entries and return a TSQLResult object containing entries following selection.
   virtual Long64_t        ReadFile(const char* filename, const char* branchDescriptor = "", char delimiter = ' ');
/// Create or simply read branches from filename.
/// if branchDescriptor = "" (default), it is assumed that the Tree descriptor
/// is given in the first line of the file with a syntax like
///     A/D:Table[2]/F:Ntracks/I:astring/C
/// otherwise branchDescriptor must be specified with the above syntax.
/// - If the type of the first variable is not specified, it is assumed to be "/F"
/// - If the type of any other variable is not specified, the type of the previous
///   variable is assumed. eg
///     - `x:y:z`      (all variables are assumed of type "F"
///     - `x/D:y:z`    (all variables are of type "D"
///     - `x:y/D:z`    (x is type "F", y and z of type "D"
/// delimiter allows for the use of another delimiter besides whitespace.
/// This provides support for direct import of common data file formats
/// like csv.  If delimiter != ' ' and branchDescriptor == "", then the
/// branch description is taken from the first line in the file, but
/// delimiter is used for the branch names tokenization rather than ':'.
/// Note however that if the values in the first line do not use the
/// /[type] syntax, all variables are assumed to be of type "F".
/// If the filename ends with extensions .csv or .CSV and a delimiter is
/// not specified (besides ' '), the delimiter is automatically set to ','.
/// Lines in the input file starting with "#" are ignored. Leading whitespace
/// for each column data is skipped. Empty lines are skipped.
/// A TBranch object is created for each variable in the expression.
/// The total number of rows read from the file is returned.

   virtual Long64_t        ReadStream(std::istream& inputStream, const char* branchDescriptor = "", char delimiter = ' ');
/// Create or simply read branches from an input stream.
/// See reference information for TTree::ReadFile

   virtual void            Refresh();
///  Refresh contents of this tree and its branches from the current status on disk.
///  One can call this function in case the tree file is being
///  updated by another process.

   virtual void            RecursiveRemove(TObject *obj);
/// Make sure that obj (which is being deleted or will soon be) is no
/// longer referenced by this TTree.

   virtual void            RemoveFriend(TTree*);/// Remove a friend from the list of friends.
   virtual void            Reset(Option_t* option = "");// Reset baskets, buffers and entries count in all branches and leaves.
   virtual void            ResetAfterMerge(TFileMergeInfo *);/// Resets the state of this TTree after a merge (keep the customization but forget the data).
   virtual void            ResetBranchAddress(TBranch *);
/// Tell all of our branches to set their addresses to zero.
/// Note: If any of our branches own any objects, they are deleted.

   virtual void            ResetBranchAddresses();/// Tell all of our branches to drop their current objects and allocate new ones.
   virtual Long64_t        Scan(const char* varexp = "", const char* selection = "", Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0); // *MENU*
// Loop over tree entries and print entries passing selection.
// If varexp is 0 (or "") then print only first 8 columns.
// If varexp = "*" print all columns.
// Otherwise a columns selection can be made using "var1:var2:var3".
// See TTreePlayer::Scan for more information

   virtual Bool_t          SetAlias(const char* aliasName, const char* aliasFormula);
/// Set a tree variable alias.
/// Set an alias for an expression/formula based on the tree 'variables'.
/// The content of 'aliasName' can be used in TTreeFormula (i.e. TTree::Draw,
/// TTree::Scan, TTreeViewer) and will be evaluated as the content of
/// 'aliasFormula'.
/// If the content of 'aliasFormula' only contains symbol names, periods and
/// array index specification (for example event.fTracks[3]), then
/// the content of 'aliasName' can be used as the start of symbol.
/// If the alias 'aliasName' already existed, it is replaced by the new value.
/// When being used, the alias can be preceded by an eventual 'Friend Alias'
/// (see TTree::GetFriendAlias)
/// Return true if it was added properly.

   virtual void            SetAutoSave(Long64_t autos = -300000000);
/// This function may be called at the start of a program to change
/// the default value for fAutoSave (and for SetAutoSave) is -300000000, ie 300 MBytes
/// When filling the Tree the branch buffers as well as the Tree header
/// will be flushed to disk when the watermark is reached.
/// If fAutoSave is positive the watermark is reached when a multiple of fAutoSave
/// entries have been written.
/// If fAutoSave is negative the watermark is reached when -fAutoSave bytes
/// have been written to the file.
/// In case of a program crash, it will be possible to recover the data in the Tree
/// up to the last AutoSave point.

   virtual void            SetAutoFlush(Long64_t autof = -30000000);
/// This function may be called at the start of a program to change
/// the default value for fAutoFlush.
/// ### CASE 1 : autof > 0
/// autof is the number of consecutive entries after which TTree::Fill will
/// flush all branch buffers to disk.
/// ### CASE 2 : autof < 0
/// When filling the Tree the branch buffers will be flushed to disk when
/// more than autof bytes have been written to the file. At the first FlushBaskets
/// TTree::Fill will replace fAutoFlush by the current value of fEntries.
/// Calling this function with autof<0 is interesting when it is hard to estimate
/// the size of one entry. This value is also independent of the Tree.
/// The Tree is initialized with fAutoFlush=-30000000, ie that, by default,
/// the first AutoFlush will be done when 30 MBytes of data are written to the file.
/// ### CASE 3 : autof = 0
/// The AutoFlush mechanism is disabled.
/// Flushing the buffers at regular intervals optimize the location of
/// consecutive entries on the disk by creating clusters of baskets.
/// A cluster of baskets is a set of baskets that contains all
/// the data for a (consecutive) set of entries and that is stored
/// consecutively on the disk.   When reading all the branches, this
/// is the minimum set of baskets that the TTreeCache will read.

   virtual void            SetBasketSize(const char* bname, Int_t buffsize = 16000);
/// Set a branch's basket size.
/// bname is the name of a branch.
/// - if bname="*", apply to all branches.
/// - if bname="xxx*", apply to all branches with name starting with xxx
/// see TRegexp for wildcarding options
/// buffsize = branc basket size

#if !defined(__CINT__)
   virtual Int_t           SetBranchAddress(const char *bname,void *add, TBranch **ptr = 0);
/// Change branch address, dealing with clone trees properly.
/// See TTree::CheckBranchAddressType for the semantic of the return value.
/// Note: See the comments in TBranchElement::SetAddress() for the
/// meaning of the addr parameter and the object ownership policy.
#endif
   virtual Int_t           SetBranchAddress(const char *bname,void *add, TClass *realClass, EDataType datatype, Bool_t isptr);
/// Verify the validity of the type of addr before calling SetBranchAddress.
/// See TTree::CheckBranchAddressType for the semantic of the return value.
/// Note: See the comments in TBranchElement::SetAddress() for the
/// meaning of the addr parameter and the object ownership policy.

   virtual Int_t           SetBranchAddress(const char *bname,void *add, TBranch **ptr, TClass *realClass, EDataType datatype, Bool_t isptr);
/// Verify the validity of the type of addr before calling SetBranchAddress.
/// See TTree::CheckBranchAddressType for the semantic of the return value.
/// Note: See the comments in TBranchElement::SetAddress() for the
/// meaning of the addr parameter and the object ownership policy.

   template <class T> Int_t SetBranchAddress(const char *bname, T **add, TBranch **ptr = 0) {
      TClass *cl = TClass::GetClass(typeid(T));
      EDataType type = kOther_t;
      if (cl==0) type = TDataType::GetType(typeid(T));
      return SetBranchAddress(bname,add,ptr,cl,type,true);
   }
#ifndef R__NO_CLASS_TEMPLATE_SPECIALIZATION
   // This can only be used when the template overload resolution can distringuish between
   // T* and T**
   template <class T> Int_t SetBranchAddress(const char *bname, T *add, TBranch **ptr = 0) {
      TClass *cl = TClass::GetClass(typeid(T));
      EDataType type = kOther_t;
      if (cl==0) type = TDataType::GetType(typeid(T));
      return SetBranchAddress(bname,add,ptr,cl,type,false);
   }
#endif
   virtual void            SetBranchStatus(const char* bname, Bool_t status = 1, UInt_t* found = 0);
/// Set branch status to Process or DoNotProcess.
/// When reading a Tree, by default, all branches are read.
/// One can speed up considerably the analysis phase by activating
/// only the branches that hold variables involved in a query.
/// bname is the name of a branch.
/// - if bname="*", apply to all branches.
/// - if bname="xxx*", apply to all branches with name starting with xxx
/// see TRegexp for wildcarding options
/// - status = 1  branch will be processed
/// - = 0  branch will not be processed
/// __WARNING! WARNING! WARNING!__
/// SetBranchStatus is matching the branch based on match of the branch
/// 'name' and not on the branch hierarchy! In order to be able to
/// selectively enable a top level object that is 'split' you need to make
/// sure the name of the top level branch is prefixed to the sub-branches'
/// name (by adding a dot ('.') at the end of the Branch creation and use the
/// corresponding bname.
/// If found is not 0, the number of branch(es) found matching the regular
/// expression is returned in *found AND the error message 'unknown branch'
/// is suppressed.

   static  void            SetBranchStyle(Int_t style = 1);  //style=0 for old branch, =1 for new branch style
   virtual Int_t           SetCacheSize(Long64_t cachesize = -1);
/// Set maximum size of the file cache .
/// - if cachesize = 0 the existing cache (if any) is deleted.
/// - if cachesize = -1 (default) it is set to the AutoFlush value when writing
///    the Tree (default is 30 MBytes).
/// Returns:
/// - 0 size set, cache was created if possible
/// - -1 on error

   virtual Int_t           SetCacheEntryRange(Long64_t first, Long64_t last);
///interface to TTreeCache to set the cache entry range
/// Returns:
/// - 0 entry range set
/// - -1 on error

   virtual void            SetCacheLearnEntries(Int_t n=10);/// Interface to TTreeCache to set the number of entries for the learning phase
   virtual void            SetChainOffset(Long64_t offset = 0) { fChainOffset=offset; }
   virtual void            SetCircular(Long64_t maxEntries);
/// Enable/Disable circularity for this tree.
/// if maxEntries > 0 a maximum of maxEntries is kept in one buffer/basket
/// per branch in memory.
///   Note that when this function is called (maxEntries>0) the Tree
///   must be empty or having only one basket per branch.
/// if maxEntries <= 0 the tree circularity is disabled.
/// #### NOTE 1:
///  Circular Trees are interesting in online real time environments
///  to store the results of the last maxEntries events.
/// #### NOTE 2:
///  Calling SetCircular with maxEntries <= 0 is necessary before
///  merging circular Trees that have been saved on files.
/// #### NOTE 3:
///  SetCircular with maxEntries <= 0 is automatically called
///  by TChain::Merge
/// #### NOTE 4:
///  A circular Tree can still be saved in a file. When read back,
///  it is still a circular Tree and can be filled again.

   virtual void            SetDebug(Int_t level = 1, Long64_t min = 0, Long64_t max = 9999999); // *MENU*
/// Set the debug level and the debug range.
/// For entries in the debug range, the functions TBranchElement::Fill
/// and TBranchElement::GetEntry will print the number of bytes filled
/// or read for each branch.

   virtual void            SetDefaultEntryOffsetLen(Int_t newdefault, Bool_t updateExisting = kFALSE);
/// Update the default value for the branch's fEntryOffsetLen.
/// If updateExisting is true, also update all the existing branches.
/// If newdefault is less than 10, the new default value will be 10.

   virtual void            SetDirectory(TDirectory* dir);
/// Change the tree's directory.
/// Remove reference to this tree from current directory and
/// add reference to new directory dir.  The dir parameter can
/// be 0 in which case the tree does not belong to any directory.

   virtual Long64_t        SetEntries(Long64_t n = -1);
/// Change number of entries in the tree.
/// If n >= 0, set number of entries in the tree = n.
/// If n < 0, set number of entries in the tree to match the
/// number of entries in each branch. (default for n is -1)
/// This function should be called only when one fills each branch
/// independently via TBranch::Fill without calling TTree::Fill.
/// Calling TTree::SetEntries() make sense only if the number of entries
/// in each branch is identical, a warning is issued otherwise.
/// The function returns the number of entries.

   virtual void            SetEstimate(Long64_t nentries = 1000000);
/// Set number of entries to estimate variable limits.
/// If n is -1, the estimate is set to be the current maximum
/// for the tree (i.e. GetEntries() + 1)
/// If n is less than -1, the behavior is undefined.

   virtual void            SetFileNumber(Int_t number = 0);
/// Set fFileNumber to number.
/// fFileNumber is used by TTree::Fill to set the file name
/// for a new file to be created when the current file exceeds fgTreeMaxSize.
///    (see TTree::ChangeFile)
/// if fFileNumber=10, the new file name will have a suffix "_11",
/// ie, fFileNumber is incremented before setting the file name

   virtual void            SetEventList(TEventList* list);
/// This function transfroms the given TEventList into a TEntryList
/// The new TEntryList is owned by the TTree and gets deleted when the tree
/// is deleted. This TEntryList can be returned by GetEntryList() function.

   virtual void            SetEntryList(TEntryList* list, Option_t *opt="");/// Set an EntryList
   virtual void            SetMakeClass(Int_t make);
/// Set all the branches in this TTree to be in decomposed object mode
/// (also known as MakeClass mode).

   virtual void            SetMaxEntryLoop(Long64_t maxev = kMaxEntries) { fMaxEntryLoop = maxev; } // *MENU*
   static  void            SetMaxTreeSize(Long64_t maxsize = 1900000000);
/// Set the maximum size in bytes of a Tree file (static function).
/// The default size is 100000000000LL, ie 100 Gigabytes.
/// In TTree::Fill, when the file has a size > fgMaxTreeSize,
/// the function closes the current file and starts writing into
/// a new file with a name of the style "file_1.root" if the original
/// requested file name was "file.root".

   virtual void            SetMaxVirtualSize(Long64_t size = 0) { fMaxVirtualSize = size; } // *MENU*
   virtual void            SetName(const char* name); // *MENU* /// Change the name of this tree.
   virtual void            SetNotify(TObject* obj) { fNotify = obj; }
   virtual void            SetObject(const char* name, const char* title);/// Change the name and title of this tree.
   virtual void            SetParallelUnzip(Bool_t opt=kTRUE, Float_t RelSize=-1);/// Enable or disable parallel unzipping of Tree buffers.
   virtual void            SetPerfStats(TVirtualPerfStats* perf);/// Set perf stats
   virtual void            SetScanField(Int_t n = 50) { fScanField = n; } // *MENU*
   virtual void            SetTimerInterval(Int_t msec = 333) { fTimerInterval=msec; }
   virtual void            SetTreeIndex(TVirtualIndex* index);
/// The current TreeIndex is replaced by the new index.
/// Note that this function does not delete the previous index.

   virtual void            SetWeight(Double_t w = 1, Option_t* option = "");
/// Set tree weight.
/// The weight is used by TTree::Draw to automatically weight each
/// selected entry in the resulting histogram.
/// This function is redefined by TChain::SetWeight. In case of a
/// TChain, an option "global" may be specified to set the same weight
/// for all trees in the TChain instead of the default behaviour
/// using the weights of each tree in the chain (see TChain::SetWeight).

   virtual void            SetUpdate(Int_t freq = 0) { fUpdate = freq; }
   virtual void            Show(Long64_t entry = -1, Int_t lenmax = 20);
/// Print values of all active leaves for entry.
/// - if entry==-1, print current entry (default)
/// - if a leaf is an array, a maximum of lenmax elements is printed.

   virtual void            StartViewer(); // *MENU*
/// Start the TTreeViewer on this tree.
/// - ww is the width of the canvas in pixels
/// - wh is the height of the canvas in pixels

   virtual Int_t           StopCacheLearningPhase();
/// Stop the cache learning phase
/// Returns:
/// - 0 learning phase stopped or not active
/// - -1 on error

   virtual Int_t           UnbinnedFit(const char* funcname, const char* varexp, const char* selection = "", Option_t* option = "", Long64_t nentries = kMaxEntries, Long64_t firstentry = 0);
/// Unbinned fit of one or more variable(s) from a tree.
/// funcname is a TF1 function.
/// See TTree::Draw for explanations of the other parameters.
/// Fit the variable varexp using the function funcname using the
/// selection cuts given by selection.
/// The list of fit options is given in parameter option.
/// - option = "Q" Quiet mode (minimum printing)
/// - option = "V" Verbose mode (default is between Q and V)
/// - option = "E" Perform better Errors estimation using Minos technique
/// - option = "M" More. Improve fit results
/// With this setup:
/// - Parameters 0->3 can vary freely
/// - Parameter 4 has boundaries [-10,-4] with initial value -8
/// - Parameter 5 is fixed to 100.
/// For the fit to be meaningful, the function must be self-normalized.
/// 1, 2 and 3 Dimensional fits are supported. See also TTree::Fit
/// Return status:
/// - The function return the status of the fit in the following form
///   fitResult = migradResult + 10*minosResult + 100*hesseResult + 1000*improveResult
/// - The fitResult is 0 is the fit is OK.
/// - The fitResult is negative in case of an error not connected with the fit.
/// - The number of entries used in the fit can be obtained via mytree.GetSelectedRows();
/// - If the number of selected entries is null the function returns -1

   void                    UseCurrentStyle();/// Replace current attributes by current style.
   virtual Int_t           Write(const char *name=0, Int_t option=0, Int_t bufsize=0);
/// Write this object to the current directory. For more see TObject::Write
/// If option & kFlushBasket, call FlushBasket before writing the tree.

   virtual Int_t           Write(const char *name=0, Int_t option=0, Int_t bufsize=0) const;
/// Write this object to the current directory. For more see TObject::Write
/// Write calls TTree::FlushBaskets before writing the tree.

code

/// You can specify boundary limits for some or all parameters via

func->SetParLimits(p_number, parmin, parmax);

/// if parmin>=parmax, the parameter is fixed

/// Note that you are not forced to fix the limits for all parameters.
/// For example, if you fit a function with 6 parameters, you can do:

func->SetParameters(0,3.1,1.e-6,0.1,-8,100);
func->SetParLimits(4,-10,-4);
func->SetParLimits(5, 1,1);

/// i.e. It must have the same integral regardless of the parameter
/// settings.  Otherwise the fit will effectively just maximize the
/// area.

/// It is mandatory to have a normalization variable
/// which is fixed for the fit.  e.g.

TF1* f1 = new TF1("f1", "gaus(0)/sqrt(2*3.14159)/[2]", 0, 5);
f1->SetParameters(1, 3.1, 0.01);
f1->SetParLimits(0, 1, 1); // fix the normalization parameter to 1
data->UnbinnedFit("f1", "jpsimass", "jpsipt>3.0");
// This gives the possibility to play with more than one index, e.g.,

TVirtualIndex* oldIndex = tree.GetTreeIndex();
tree.SetTreeIndex(newIndex);
tree.Draw();
tree.SetTreeIndex(oldIndex);
tree.Draw(); etc
/// Assume a tree T with sub-branches a,b,c,d,e,f,g,etc..
/// when doing T.GetEntry(i) all branches are read for entry i.
/// to read only the branches c and e, one can do

T.SetBranchStatus("*",0); //disable all branches
T.SetBranchStatus("c",1);
T.setBranchStatus("e",1);
T.GetEntry(i);

/// bname is interpreted as a wildcarded TRegexp (see TRegexp::MakeWildcard).
/// Thus, "a*b" or "a.*b" matches branches starting with "a" and ending with
/// "b", but not any other branch with an "a" followed at some point by a
/// "b". For this second behavior, use "*a*b*". Note that TRegExp does not
/// support '|', and so you cannot select, e.g. track and shower branches
/// with "track|shower".

/// I.e If your Tree has been created in split mode with a parent branch "parent."
/// (note the trailing dot).

T.SetBranchStatus("parent",1);

/// will not activate the sub-branches of "parent". You should do:

T.SetBranchStatus("parent*",1);

/// Without the trailing dot in the branch creation you have no choice but to
/// call SetBranchStatus explicitly for each of the sub branches.

/// An alternative to this function is to read directly and only
/// the interesting branches. Example:

TBranch *brc = T.GetBranch("c");
TBranch *bre = T.GetBranch("e");
brc->GetEntry(i);
bre->GetEntry(i);
tree->SetAlias("x1","(tdc1[1]-tdc1[0])/49");
tree->SetAlias("y1","(tdc1[3]-tdc1[2])/47");
tree->SetAlias("x2","(tdc2[1]-tdc2[0])/49");
tree->SetAlias("y2","(tdc2[3]-tdc2[2])/47");
tree->Draw("y2-y1:x2-x1");

tree->SetAlias("theGoodTrack","event.fTracks[3]");
tree->Draw("theGoodTrack.fPx"); // same as "event.fTracks[3].fPx"
/// To fill a TTree with multiple input text files, proceed as indicated above
/// for the first input file and omit the second argument for subsequent calls

T.ReadFile("file1.dat","branch descriptor");
T.ReadFile("file2.dat");
/// ## NOTE1
/// It may be more interesting to invoke directly the other Process function
/// accepting a TSelector* as argument.eg

MySelector *selector = (MySelector*)TSelector::GetSelector(filename);
selector->CallSomeFunction(..);
mytree.Process(selector,..);

/// ## NOTE2
/// One should not call this function twice with the same selector file
/// in the same script. If this is required, proceed as indicated in NOTE1,
/// by getting a pointer to the corresponding TSelector,eg

void stubs1() {
   TSelector *selector = TSelector::GetSelector("h1test.C");
   TFile *f1 = new TFile("stubs_nood_le1.root");
   TTree *h1 = (TTree*)f1->Get("h1");
   h1->Process(selector);
   TFile *f2 = new TFile("stubs_nood_le1_coarse.root");
    TTree *h2 = (TTree*)f2->Get("h1");
    h2->Process(selector);
}

/// or use ACLIC to compile the selector

void stubs2() {
    TFile *f1 = new TFile("stubs_nood_le1.root");
    TTree *h1 = (TTree*)f1->Get("h1");
    h1->Process("h1test.C+");
   TFile *f2 = new TFile("stubs_nood_le1_coarse.root");
   TTree *h2 = (TTree*)f2->Get("h1");
   h2->Process("h1test.C+");
}
/// you can retrieve a pointer to the created object via:

TPrincipal *principal = (TPrincipal*)gROOT->GetListOfSpecials()->FindObject("principal");
/// For example with Event.root, if

Double_t somePx = fTracks.fPx[2];

/// is executed by one of the method of the skeleton,
/// somePx will updated with the current value of fPx of the 3rd track.

/// Both macrofilename and the optional cutfilename are expected to be
/// the name of source files which contain at least a free standing
/// function with the signature:

x_t macrofilename(); // i.e function with the same name as the file

/// and

y_t cutfilename();   // i.e function with the same name as the file

/// x_t and y_t needs to be types that can convert respectively to a double
/// and a bool (because the skeleton uses:

if (cutfilename()) htemp->Fill(macrofilename());

/// These two functions are run in a context such that the branch names are
/// available as local variables of the correct (read-only) type.

/// Note that if you use the same 'variable' twice, it is more efficient
/// to 'cache' the value. For example:

Int_t n = fEventNumber; // Read fEventNumber
if (n<10 || n>10) { ... }

/// is more efficient than

if (fEventNumber<10 || fEventNumber>10)

/// Also, optionally, the generated selector will also call methods named
/// macrofilename_methodname in each of 6 main selector methods if the method
/// macrofilename_methodname exist (Where macrofilename is stripped of its
/// extension).

/// To draw px using the file hsimple.root (generated by the
/// hsimple.C tutorial), we need a file named hsimple.cxx:

double hsimple() {
   return px;
}

/// MakeProxy can then be used indirectly via the TTree::Draw interface
/// as follow:

new TFile("hsimple.root")
ntuple->Draw("hsimple.cxx");
/// To use this function:
/// - Open your tree file (eg: TFile f("myfile.root");)
/// - T->MakeClass("MyClass");

/// where T is the name of the TTree in file myfile.root,
/// and MyClass.h, MyClass.C the name of the files created by this function.
/// In a ROOT session, you can do:

root > .L MyClass.C
root > MyClass* t = new MyClass;
root > t->GetEntry(12); // Fill data members of t with entry number 12.
root > t->Show();       // Show values of entry 12.
root > t->Show(16);     // Read and show values of entry 16.
root > t->Loop();       // Loop on all entries.
/// To activate/deactivate one or more branches, use TBranch::SetBranchStatus
/// For example, if you have a Tree with several hundred branches, and you
/// are interested only by branches named "a" and "b", do

mytree.SetBranchStatus("*",0); //disable all branches
mytree.SetBranchStatus("a",1);
mytree.SetBranchStatus("b",1);

/// when calling mytree.GetEntry(i); only branches "a" and "b" will be read.

/// __WARNING!!__
/// If your Tree has been created in split mode with a parent branch "parent.",

mytree.SetBranchStatus("parent",1);

/// will not activate the sub-branches of "parent". You should do:

mytree.SetBranchStatus("parent*",1);

/// Without the trailing dot in the branch creation you have no choice but to
/// call SetBranchStatus explicitly for each of the sub branches.

/// An alternative is to call directly

brancha.GetEntry(i)
branchb.GetEntry(i);


/// Consider the example in $ROOTSYS/test/Event.h
/// The top level branch in the tree T is declared with:

Event *event = 0;  //event must be null or point to a valid object
                   //it must be initialized
T.SetBranchAddress("event",&event);

/// When reading the Tree, one can choose one of these 3 options:
///
/// ## OPTION 1

for (Long64_t i=0;i<nentries;i++) {
   T.GetEntry(i);
   // the object event has been filled at this point
}

/// The default (recommended). At the first entry an object of the class
/// Event will be created and pointed by event. At the following entries,
/// event will be overwritten by the new data. All internal members that are
/// TObject* are automatically deleted. It is important that these members
/// be in a valid state when GetEntry is called. Pointers must be correctly
/// initialized. However these internal members will not be deleted if the
/// characters "->" are specified as the first characters in the comment
/// field of the data member declaration.
///
/// If "->" is specified, the pointer member is read via pointer->Streamer(buf).
/// In this case, it is assumed that the pointer is never null (case of
/// pointer TClonesArray *fTracks in the Event example). If "->" is not
/// specified, the pointer member is read via buf >> pointer. In this case
/// the pointer may be null. Note that the option with "->" is faster to
/// read or write and it also consumes less space in the file.
///
/// ## OPTION 2
///
/// The option AutoDelete is set

TBranch *branch = T.GetBranch("event");
branch->SetAddress(&event);
branch->SetAutoDelete(kTRUE);
for (Long64_t i=0;i<nentries;i++) {
   T.GetEntry(i);
   // the object event has been filled at this point
}

/// In this case, at each iteration, the object event is deleted by GetEntry
/// and a new instance of Event is created and filled.

/// ## OPTION 3

/// Same as option 1, but you delete yourself the event.

for (Long64_t i=0;i<nentries;i++) {
   delete event;
   event = 0;  // EXTREMELY IMPORTANT
   T.GetEntry(i);
    // the object event has been filled at this point
}

/// It is strongly recommended to use the default option 1. It has the
/// additional advantage that functions like TTree::Draw (internally calling
/// TTree::GetEntry) will be functional even when the classes in the file are
/// not available.

/// Note: See the comments in TBranchElement::SetAddress() for the
/// object ownership policy of the underlying (user) data.
TTree::TClusterIterator clusterIter = tree->GetClusterIterator(entry);
Long64_t clusterStart;
while( (clusterStart = clusterIter()) < tree->GetEntries() ) {
   printf("The cluster starts at %lld and ends at %lld (inclusive)\n",clusterStart,clusterIter.GetNextEntry()-1);
}
tree.Fit(pol4,sqrt(x)>>hsqrt,y>0)

/// will fit sqrt(x) and save the histogram as "hsqrt" in the current
/// directory.

/// See also TTree::UnbinnedFit
// virtual Int_t           Branch(TCollection* list, Int_t bufsize = 32000, Int_t splitlevel = 99, const char* name = "");

{
      TTree T("T","test list");
      TList *list = new TList();

      TObjArray *a1 = new TObjArray();
      a1->SetName("a1");
      list->Add(a1);
      TH1F *ha1a = new TH1F("ha1a","ha1",100,0,1);
      TH1F *ha1b = new TH1F("ha1b","ha1",100,0,1);
      a1->Add(ha1a);
      a1->Add(ha1b);
      TObjArray *b1 = new TObjArray();
      b1->SetName("b1");
      list->Add(b1);
      TH1F *hb1a = new TH1F("hb1a","hb1",100,0,1);
      TH1F *hb1b = new TH1F("hb1b","hb1",100,0,1);
      b1->Add(hb1a);
      b1->Add(hb1b);

      TObjArray *a2 = new TObjArray();
      a2->SetName("a2");
      list->Add(a2);
      TH1S *ha2a = new TH1S("ha2a","ha2",100,0,1);
      TH1S *ha2b = new TH1S("ha2b","ha2",100,0,1);
      a2->Add(ha2a);
      a2->Add(ha2b);

      T.Branch(list,16000,2);
      T.Print();
}
// virtual Long64_t        AutoSave(Option_t* option = "");

void treew() {
   TFile f("test.root","recreate");
   TNtuple *ntuple = new TNtuple("ntuple","Demo","px:py:pz:random:i");
   Float_t px, py, pz;
   for ( Int_t i=0; i<10000000; i++) {
      gRandom->Rannor(px,py);
      pz = px*px + py*py;
      Float_t random = gRandom->Rndm(1);
      ntuple->Fill(px,py,pz,random,i);
      if (i%1000 == 1) ntuple->AutoSave("SaveSelf");
   }
}

void treer() {
   TFile f("test.root");
   TTree *ntuple = (TTree*)f.Get("ntuple");
   TCanvas c1;
   Int_t first = 0;
   while(1) {
      if (first == 0) ntuple->Draw("px>>hpx", "","",10000000,first);
      else            ntuple->Draw("px>>+hpx","","",10000000,first);
      first = (Int_t)ntuple->GetEntries();
      c1.Update();
      gSystem->Sleep(1000); //sleep 1 second
      ntuple->Refresh();
   }
}
// You may want to add a branch to an existing tree. For example,
// if one variable in the tree was computed with a certain algorithm,
// you may want to try another algorithm and compare the results.
// One solution is to add a new branch, fill it, and save the tree.
// The code below adds a simple branch to an existing tree.
// Note the kOverwrite option in the Write method, it overwrites the
// existing tree. If it is not specified, two copies of the tree headers
// are saved.

void tree3AddBranch() {
TFile f("tree3.root", "update");

Float_t new_v;
TTree *t3 = (TTree*)f->Get("t3");
TBranch *newBranch = t3->Branch("new_v", &new_v, "new_v/F");

Long64_t nentries = t3->GetEntries(); // read the number of entries in the t3

for (Long64_t i = 0; i < nentries; i++) {
new_v= gRandom->Gaus(0, 1);
newBranch->Fill();
}

t3->Write("", TObject::kOverwrite); // save only the new version of the tree
}

// Adding a branch is often not possible because the tree is in a read-only
// file and you do not have permission to save the modified tree with the
// new branch. Even if you do have the permission, you risk losing the
// original tree with an unsuccessful attempt to save  the modification.
// Since trees are usually large, adding a branch could extend it over the
// 2GB limit. In this case, the attempt to write the tree fails, and the
// original data is erased.
// In addition, adding a branch to a tree enlarges the tree and increases
// the amount of memory needed to read an entry, and therefore decreases
// the performance.
// Store data from tree to vector
t->SetEstimate(-1);
t->Draw("energy");
std::vector<Double_t> Vals(t->GetV1(), t->GetV1() + t->GetSelectedRows());

写数据的同时另一个程序读取

// The use of the non-default TObject::kOverwrite is fatal in this case. TObject::kOverwrite is an explicit to first remove the previous copy and then write the new copy (lightly in place of the hold one) into the file. This significantly increase the risk that the writing happens while the reader in not yet done reading.
// If you want the write the object safely while still disabling the keeping of cycle (backup copy) use TObject::kWriteDelete (which write then deletes).
// You can also use SaveSelf rather than Flush but then need to explicitly store each historgram.
#include "TFile.h"
#include "TH1F.h"

void writer() {
   TFile *f = new TFile("test.root","RECREATE");
   TH1F *h = new TH1F("h","h",100,-2,2);
   f->Write(0,TObject::kReadWrite);
   int count = 0;
   while(1) {
      printf("Loop %d\r",count++);
      fflush(stdout);
      h->FillRandom("gaus",100);
      h->Write(0,TObject::kReadWrite);
      f->SaveSelf();
      sleep(1);
   }
}

// To refresh the information on the reader side, use ReadKeys:

void reading(const TFile *f, const char *name="gaus") {
   f->ReadKeys();
   delete f->FindObject(name);
   TH1F *h;  f->GetObject(name,h);
   h->Draw();
}

example

    // A simple example with histograms and a tree
    //
    // This program creates :
    //    - a one dimensional histogram
    //    - a two dimensional histogram
    //    - a profile histogram
    //    - a tree
    //
    // These objects are filled with some random numbers and saved on a file.

    #include "TFile.h"
    #include "TH1.h"
    #include "TH2.h"
    #include "TProfile.h"
    #include "TRandom.h"
    #include "TTree.h"

    //__________________________________________________________________________
    main(int argc, char **argv)
    {
    // Create a new ROOT binary machine independent file.
    // Note that this file may contain any kind of ROOT objects, histograms,trees
    // pictures, graphics objects, detector geometries, tracks, events, etc..
    // This file is now becoming the current directory.
    TFile hfile("htree.root","RECREATE","Demo ROOT file with histograms & trees");

    // Create some histograms and a profile histogram
    TH1F *hpx   = new TH1F("hpx","This is the px distribution",100,-4,4);
    TH2F *hpxpy = new TH2F("hpxpy","py ps px",40,-4,4,40,-4,4);
    TProfile *hprof = new TProfile("hprof","Profile of pz versus px",100,-4,4,0,20);

    // Define some simple structures
    typedef struct {Float_t x,y,z;} POINT;
    typedef struct {
       Int_t ntrack,nseg,nvertex;
       UInt_t flag;
       Float_t temperature;
    } EVENTN;
    static POINT point;
    static EVENTN eventn;

    // Create a ROOT Tree
    TTree *tree = new TTree("T","An example of ROOT tree with a few branches");
    tree->Branch("point",&point,"x:y:z");
    tree->Branch("eventn",&eventn,"ntrack/I:nseg:nvertex:flag/i:temperature/F");
    tree->Branch("hpx","TH1F",&hpx,128000,0);

    Float_t px,py,pz;
    static Float_t p[3];

    // Here we start a loop on 1000 events
    for ( Int_t i=0; i<1000; i++) {
       gRandom->Rannor(px,py);
       pz = px*px + py*py;
       Float_t random = gRandom->::Rndm(1);

       // Fill histograms
       hpx->Fill(px);
       hpxpy->Fill(px,py,1);
       hprof->Fill(px,pz,1);

       // Fill structures
       p[0] = px;
       p[1] = py;
       p[2] = pz;
       point.x = 10*(random-1);;
       point.y = 5*random;
       point.z = 20*random;
       eventn.ntrack  = Int_t(100*random);
       eventn.nseg    = Int_t(2*eventn.ntrack);
       eventn.nvertex = 1;
       eventn.flag    = Int_t(random+0.5);
       eventn.temperature = 20+random;

       // Fill the tree. For each event, save the 2 structures and 3 objects
       // In this simple example, the objects hpx, hprof and hpxpy are slightly
       // different from event to event. We expect a big compression factor!
       tree->Fill();
    }
    // End of the loop

    tree->Print();

    // Save all objects in this file
    hfile.Write();

    // Close the file. Note that this is automatically done when you leave
    // the application.
    hfile.Close();

    return 0;
}
© Hongyi Wu            updated: 2019-03-31 18:50:01

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