TChain

class TChain : public TTree

    public:

                       TChain TChain()
                       TChain TChain(const char* name, const char* title)
                 virtual void ~TChain()
                virtual Int_t Add(TChain* chain)
                virtual Int_t Add(const char* name, Int_t nentries = kBigNumber)
                virtual Int_t AddFile(const char* name, Int_t nentries)
      virtual TFriendElement* AddFriend(const char* chainname, const char* dummy)
      virtual TFriendElement* AddFriend(const char* chainname, TFile* dummy)
      virtual TFriendElement* AddFriend(TTree* chain, const char* alias, Bool_t warn = kFALSE)
                 virtual void Browse(TBrowser* b)
               static TClass* Class()
                 virtual void CreatePackets()
                 virtual void Draw(Option_t* opt)
                virtual Int_t Draw(const char* varexp, const TCut& selection, Option_t* option, Int_t nentries = kBigNumber, Int_t firstentry = 0)
                virtual Int_t Draw(const char* varexp, const char* selection, Option_t* option, Int_t nentries = kBigNumber, Int_t firstentry = 0)
                virtual Int_t Fill()
             virtual TBranch* GetBranch(const char* name)
                virtual Int_t GetChainEntryNumber(Int_t entry) const
             virtual Double_t GetEntries() const
                virtual Int_t GetEntry(Int_t entry = 0, Int_t getall = 0)
                       TFile* GetFile() const
               virtual TLeaf* GetLeaf(const char* name)
           virtual TObjArray* GetListOfBranches()
                   TObjArray* GetListOfFiles() const
           virtual TObjArray* GetListOfLeaves()
             virtual Double_t GetMaximum(const char* columname)
             virtual Double_t GetMinimum(const char* columname)
                virtual Int_t GetNbranches()
                        Int_t GetNtrees() const
                       TList* GetStatus() const
               virtual TTree* GetTree() const
                virtual Int_t GetTreeNumber() const
                       Int_t* GetTreeOffset() const
                        Int_t GetTreeOffsetLen() const
             virtual Double_t GetWeight() const
              virtual TClass* IsA() const
                virtual Int_t LoadTree(Int_t entry)
                 virtual void Loop(Option_t* option, Int_t nentries = kBigNumber, Int_t firstentry = 0)
                 virtual void ls(Option_t* option) const
                virtual Int_t Merge(const char* name)
                virtual Int_t Merge(TFile* file, Int_t basketsize, Option_t* option)
                 virtual void Print(Option_t* option) const
                virtual Int_t Process(const char* filename, Option_t* option, Int_t nentries = kBigNumber, Int_t firstentry = 0)
                virtual Int_t Process(TSelector* selector, Option_t* option, Int_t nentries = kBigNumber, Int_t firstentry = 0)
                 virtual void Reset(Option_t* option)
                 virtual void SetAutoDelete(Bool_t autodel = kTRUE)
                 virtual void SetBranchAddress(const char* bname, void* add)
                 virtual void SetBranchStatus(const char* bname, Bool_t status = 1)
                 virtual void SetDirectory(TDirectory* dir)
                 virtual void SetMakeClass(Int_t make)
                 virtual void SetPacketSize(Int_t size = 100)
                 virtual void SetWeight(Double_t w = 1, Option_t* option)
                 virtual void ShowMembers(TMemberInspector& insp, char* parent)
                 virtual void Streamer(TBuffer& b)
                         void StreamerNVirtual(TBuffer& b)
                 virtual void UseCache(Int_t maxCacheSize = 10, Int_t pageSize = TCache::kDfltPageSize)

Data Members

    protected:

           Int_t fTreeOffsetLen  Current size of fTreeOffset array
           Int_t fNtrees         Number of Trees
           Int_t fTreeNumber     ! Current Tree number in fTreeOffset table
          Int_t* fTreeOffset     [fTreeOffsetLen]Array of variables
           Int_t fMaxCacheSize   ! Max cache size passed to TFile's
           Int_t fPageSize       ! Cache page size passed to TFile's
          TTree* fTree           ! Pointer to current tree
          TFile* fFile           ! Pointer to current file
      TObjArray* fFiles          ->  List of file names containing the Trees
          TList* fStatus         ->  List of active/inactive branches

    public:

      static const enum TChain:: kGlobalWeight  
      static const enum TChain:: kAutoDelete    
      static const enum TChain:: kBigNumber     

Class Description

                                                                      
 TChain                                                               
                                                                      
 A chain is a collection of files containg TTree objects.             
 When the chain is created, the first parameter is the default name   
 for the Tree to be processed later on.                               
                                                                      
 Enter a new element in the chain via the TChain::Add function.       
 Once a chain is defined, one can use the normal TTree functions      
 to Draw,Scan,etc.                                                    
                                                                      
 Use TChain::SetBranchStatus to activate one or more branches for all 
 the trees in the chain.                                              
                                                                      

*-*-*-*-*-*Default constructor for Chain*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*        ==============================

*-*-*-*-*-*-*-*-*-*-*-*-*Create a Chain*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*                      ==============

   A TChain is a collection of TFile objects.
    the first parameter "name" is the name of the TTree object
    in the files added with Add.
   Use TChain::Add to add a new element to this chain.

   In case the Tree is in a subdirectory, do, eg:
     TChain ch("subdir/treename");

    Example:
  Suppose we have 3 files f1.root, f2.root and f3.root. Each file
  contains a TTree object named "T".
     TChain ch("T");  creates a chain to process a Tree called "T"
     ch.Add("f1.root");
     ch.Add("f2.root");
     ch.Add("f3.root");
     ch.Draw("x");
       The Draw function above will process the variable "x" in Tree "T"
       reading sequentially the 3 files in the chain ch.

*-*

 destructor for a Chain

 Add all files referenced by the TChain chain to this chain.

 Add a new file to this chain.
 Argument name may have the following format:
   //machine/file_name.root/subdir/tree_name
 machine, subdir and tree_name are optional. If tree_name is missing,
 the chain name will be assumed.
 Name may use the wildcarding notation, eg "xxx*.root" means all files
 starting with xxx in the current file system directory.
 NB. To add all the files of a TChain to a chain, use Add(TChain *chain).

    A- if nentries <= 0, the file is connected and the tree header read
       in memory to get the number of entries.

    B- if (nentries > 0, the file is not connected, nentries is assumed to be
       the number of entries in the file. In this case, no check is made that
       the file exists and the Tree existing in the file. This second mode
       is interesting in case the number of entries in the file is already stored
       in a run data base for example.

    C- if (nentries == kBigNumber) (default), the file is not connected.
       the number of entries in each file will be read only when the file
       will need to be connected to read an entry.
       This option is the default and very efficient if one process
       the chain sequentially. Note that in case TChain::GetEntry(entry)
       is called and entry refers to an entry in the 3rd file, for example,
       this forces the Tree headers in the first and second file
       to be read to find the number of entries in these files.
       Note that if one calls TChain::GetEntriesFast() after having created
       a chain with this default, GetEntriesFast will return kBigNumber!
       TChain::GetEntries will force of the Tree headers in the chain to be
       read to read the number of entries in each Tree.

       Add a new file to this chain.

    A- if nentries <= 0, the file is connected and the tree header read
       in memory to get the number of entries.

    B- if (nentries > 0, the file is not connected, nentries is assumed to be
       the number of entries in the file. In this case, no check is made that
       the file exists and the Tree existing in the file. This second mode
       is interesting in case the number of entries in the file is already stored
       in a run data base for example.

    C- if (nentries == kBigNumber) (default), the file is not connected.
       the number of entries in each file will be read only when the file
       will need to be connected to read an entry.
       This option is the default and very efficient if one process
       the chain sequentially. Note that in case TChain::GetEntry(entry)
       is called and entry refers to an entry in the 3rd file, for example,
       this forces the Tree headers in the first and second file
       to be read to find the number of entries in these files.
       Note that if one calls TChain::GetEntriesFast() after having created
       a chain with this default, GetEntriesFast will return kBigNumber!
       TChain::GetEntries will force of the Tree headers in the chain to be
       read to read the number of entries in each Tree.

 Add a TFriendElement to the list of friends of this chain.

   A TChain has a list of friends similar to a tree (see TTree::AddFriend).
 You can add a friend to a chain with the TChain::AddFriend method, and you
 can retrieve the list of friends with TChain::GetListOfFriends.
 This example has four chains each has 20 ROOT trees from 20 ROOT files.

 TChain ch("t"); // a chain with 20 trees from 20 files
 TChain ch1("t1");
 TChain ch2("t2");
 TChain ch3("t3");
 Now we can add the friends to the first chain.

 ch.AddFriend("t1")
 ch.AddFriend("t2")
 ch.AddFriend("t3")


/*

*/


 The parameter is the name of friend chain (the name of a chain is always
 the name of the tree from which it was created).
 The original chain has access to all variable in its friends.
 We can use the TChain::Draw method as if the values in the friends were
 in the original chain.
 To specify the chain to use in the Draw method, use the syntax:

 <chainname>.<branchname>.<varname>
 If the variable name is enough to uniquely identify the variable, you can
 leave out the chain and/or branch name.
 For example, this generates a 3-d scatter plot of variable "var" in the
 TChain ch versus variable v1 in TChain t1 versus variable v2 in TChain t2.

 ch.Draw("var:t1.v1:t2.v2");
 When a TChain::Draw is executed, an automatic call to TTree::AddFriend
 connects the trees in the chain. When a chain is deleted, its friend
 elements are also deleted.

 The number of entries in the friend must be equal or greater to the number
 of entries of the original chain. If the friend has fewer entries a warning
 is given and the resulting histogram will have missing entries.
 For additional information see TTree::AddFriend.

 Initialize the packet descriptor string

 Draw expression varexp for selected entries.

 This function accepts TCut objects as arguments.
 Useful to use the string operator +, example:
    ntuple.Draw("x",cut1+cut2+cut3);

 Process all entries in this chain and draw histogram
 corresponding to expression varexp.

 Return pointer to the branch name in the current tree

 return absolute entry number in the chain
 the input parameter entry is the entry number in the current Tree of this chain

 return the total number of entries in the chain.
 In case the number of entries in each tree is not yet known,
 the offset table is computed

 Get entry from the file to memory

     getall = 0 : get only active branches
     getall = 1 : get all branches

 return the total number of bytes read

  Return pointer to the leaf name in the current tree

 Return pointer to list of branches of current tree

 Return pointer to list of leaves of current tree

 Return maximum of column with name columname

 Return minimum of column with name columname

 Return number of branches of current tree

  return the chain weight.
  by default, the weight is the weight of the current Tree in the TChain.
  However, if the weight has been set in TChain::SetWeight with
  the option "global", each Tree will use the same weight stored
  in TChain::fWeight.

  The input argument entry is the entry serial number in the whole chain.
  The function finds the corresponding Tree and returns the entry number
  in this tree.

 Loop on nentries of this chain starting at firstentry

 Merge all files in this chain into a new file.
 See important note in the following function Merge().

     Merge all files in this chain into a new file
     if option ="C" is given, the compression level for all branches
        in the new Tree is set to the file compression level.
     By default, the compression level of all branches is the
     original compression level in the old Trees.

     if (basketsize > 1000, the basket size for all branches of the
     new Tree will be set to basketsize.

 IMPORTANT Note 1: Before invoking this function, the branch addresses
            of the TTree must have been set.
  example using the file generated in $ROOTSYS/test/Event
  merge two copies of Event.root

        gSystem.Load("libEvent");
        Event *event = new Event();
        TChain ch("T");
        ch.SetBranchAddress("event",&event);
        ch.Add("Event1.root");
        ch.Add("Event2.root");
        ch.Merge("all.root");

  The SetBranchAddress statement is not necessary if the Tree
  contains only basic types (case of files converted from hbook)
  NOTE that the merged Tree contains only the active branches.

 IMPORTANT Note 2: AUTOMATIC FILE OVERFLOW
 -----------------------------------------
 When merging many files, it may happen that the resulting file
 reaches a size > TTree::fgMaxTreeSize (default = 1.9 GBytes). In this case
 the current file is automatically closed and a new file started.
 If the name of the merged file was "merged.root", the subsequent files
 will be named "merged_1.root", "merged_2.root", etc.
 fgMaxTreeSize may be modified via the static function TTree::SetMaxTreeSize.

 IMPORTANT Note 3: The input file is automatically closed and deleted.
 This is required because in general the automatic file overflow described
 above may happen during the merge.

 The function returns the total number of files produced.

 Print the header information of each Tree in the chain.
 see TTree::Print for a list of options

 Process all entries in this chain, calling functions in filename
 see TTree::Process

 Process this chain executing the code in selector

 Resets the definition of this chain

  Set the global branch kAutoDelete bit
  When LoadTree loads a new Tree, the branches for which
  the address is set will have the option AutoDelete set
  For more details on AutoDelete, see TBranch::SetAutoDelete.

 Set branch address

      bname is the name of a branch.
      add is the address of the branch.

 Set branch status Process or DoNotProcess

      bname is the name of a branch. if bname="*", apply to all branches.
      status = 1  branch will be processed
             = 0  branch will not be processed

 Remove reference to this chain from current directory and add
 reference to new directory dir. dir can be 0 in which case the chain
 does not belong to any directory.

 Set number of entries per packet for parallel root

  Set chain weight.
  The weight is used by TTree::Draw to automatically weight each
  selected entry in the resulting histogram.
  For example the equivalent of
     chain.Draw("x","w")
  is
     chain.SetWeight(w,"global");
     chain.Draw("x");

  By default the weight used will be the weight
  of each Tree in the TChain. However, one can force the individual
  weights to be ignored by specifying the option "global".
  In this case, the TChain global weight will be used for all Trees.

 Stream a class object

 Activate file caching. Use maxCacheSize to specify the maximum cache size
 in MB's (default is 10 MB) and pageSize to specify the page size
 (default is 512 KB). To turn off the cache use maxCacheSize=0.
 Not needed for normal disk files since the operating system will
 do proper caching (via the "buffer cache"). Use it for TNetFile,
 TWebFile, TRFIOFile, TDCacheFile, etc.

Inline Functions

              Int_t Draw(const char* varexp, const char* selection, Option_t* option, Int_t nentries = kBigNumber, Int_t firstentry = 0)
              Int_t Fill()
              Int_t GetNtrees() const
             TFile* GetFile() const
         TObjArray* GetListOfFiles() const
             TList* GetStatus() const
             TTree* GetTree() const
              Int_t GetTreeNumber() const
             Int_t* GetTreeOffset() const
              Int_t GetTreeOffsetLen() const
               void SetMakeClass(Int_t make)
            TClass* Class()
            TClass* IsA() const
               void ShowMembers(TMemberInspector& insp, char* parent)
               void StreamerNVirtual(TBuffer& b)