library: libTree #include "TChain.h"

# TChain

class description - source file - inheritance tree (.pdf)

## class TChain : public TTree

| Inheritance Chart:

`TObject`

<-

`TNamed`

`TAttLine`

`TAttFill`

`TAttMarker`

<-

`TTree`

<-

`TChain`

        protected:

          void ReleaseChainProof()

        public:

                                  TChain()
                                  TChain(const char* name, const char* title = "")
                          virtual ~TChain()
                    virtual Int_t Add(TChain* chain)
                    virtual Int_t Add(const char* name, Long64_t nentries = kBigNumber)
                    virtual Int_t AddFile(const char* name, Long64_t nentries = kBigNumber, const char* tname = "")
          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)
                     virtual void CanDeleteRefs(Bool_t flag = kTRUE)
                   static TClass* Class()
                     virtual void CreatePackets()
                 virtual Long64_t Draw(const char* varexp, const TCut& selection, Option_t* option = "", Long64_t nentries = kBigNumber, Long64_t firstentry = 0)
                 virtual Long64_t Draw(const char* varexp, const char* selection, Option_t* option = "", Long64_t nentries = kBigNumber, Long64_t firstentry = 0)
                     virtual void Draw(Option_t* opt)
                    virtual Int_t Fill()
                 virtual TBranch* FindBranch(const char* name)
                   virtual TLeaf* FindLeaf(const char* name)
              virtual const char* GetAlias(const char* aliasName) const
                 virtual TBranch* GetBranch(const char* name)
                   virtual Bool_t GetBranchStatus(const char* branchname) const
                 virtual Long64_t GetChainEntryNumber(Long64_t entry) const
                 virtual Long64_t GetEntries() const
                    virtual Int_t GetEntry(Long64_t entry = 0, Int_t getall = 0)
                    virtual Int_t GetEntryWithIndex(Int_t major, Int_t minor = 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
                 virtual Long64_t GetReadEntry() const
                           TList* GetStatus() const
                   virtual TTree* GetTree() const
                    virtual Int_t GetTreeNumber() const
                        Long64_t* GetTreeOffset() const
                            Int_t GetTreeOffsetLen() const
                 virtual Double_t GetWeight() const
                  virtual TClass* IsA() const
                    virtual Int_t LoadBaskets(Long64_t maxmemory)
                 virtual Long64_t LoadTree(Long64_t entry)
                     virtual void Loop(Option_t* option = "", Long64_t nentries = kBigNumber, Long64_t firstentry = 0)
                     virtual void ls(Option_t* option = "") const
                 virtual Long64_t Merge(const char* name)
                 virtual Long64_t Merge(TCollection* list)
                 virtual Long64_t Merge(TFile* file, Int_t basketsize, Option_t* option = "")
                     virtual void Print(Option_t* option = "") const
                 virtual Long64_t Process(const char* filename, Option_t* option = "", Long64_t nentries = kBigNumber, Long64_t firstentry = 0)
                 virtual Long64_t Process(TSelector* selector, Option_t* option = "", Long64_t nentries = kBigNumber, Long64_t firstentry = 0)
                     virtual void Reset(Option_t* option = "")
                 virtual Long64_t Scan(const char* varexp = "", const char* selection = "", Option_t* option = "", Long64_t nentries = 1000000000, Long64_t firstentry = 0)
                     virtual void SetAutoDelete(Bool_t autodel = kTRUE)
                     virtual void SetBranchAddress(const char* bname, void* add)
                     virtual void SetBranchAddress(const char* bname, void* add, TClass* realClass, EDataType datatype, Bool_t ptr)
                     virtual void SetBranchStatus(const char* bname, Bool_t status = 1, UInt_t* found = 0)
                     virtual void SetDirectory(TDirectory* dir)
                     virtual void SetMakeClass(Int_t make)
                     virtual void SetPacketSize(Int_t size = 100)
                     virtual void SetProof(TVirtualProof* proof = (TVirtualProof*)-1)
                     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
             Long64_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
                Bool_t fCanDeleteRefs  ! if true, TProcessIDs are deleted when closing a file
                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
          TChainProof* fChainProof     ! wrapper class for a TDSet if this chain is to be

        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.

TChain(): TTree()

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

TChain(const char *name, const char *title) :TTree(name,title)

    *-*-*-*-*-*-*-*-*-*-*-*-*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.

    *-*

~TChain()

     destructor for a Chain

Int_t Add(TChain *chain)

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

Int_t Add(const char *name, Long64_t nentries)

     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.

Int_t AddFile(const char *name, Long64_t nentries, const char *tname)

           Add a new file to this chain.
           if tname is specified, the chain will load the tree named tname
           from the file, otherwise the original treename specified in the
           TChain constructor will be used.

        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.

TFriendElement* AddFriend(const char *chain, const char *dummy)

     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.

TFriendElement* AddFriend(const char *chain, TFile *dummy)

TFriendElement* AddFriend(TTree *chain, const char* alias, Bool_t /*warn*/)

void Browse(TBrowser *)

void CanDeleteRefs(Bool_t flag)

     when closing a file during the chain processing, the file
     may be closed with option "R" if flag is set to kTRUE.
     by default flag is kTRUE.
     When closing a file with option "R", all TProcessIDs referenced by this
     file are deleted.
     Calling TFile::Close("R") might be necessary in case one reads a long list
     of files having TRef, writing some of the referenced objects or TRef
     to a new file. If the TRef or referenced objects of the file being closed
     will not be referenced again, it is possible to minimize the size
     of the TProcessID data structures in memory by forcing a delete of
     the unused TProcessID.

void CreatePackets()

     Initialize the packet descriptor string

Long64_t Draw(const char *varexp, const TCut &selection, Option_t *option, Long64_t nentries, Long64_t firstentry)

     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);

Long64_t Draw(const char *varexp, const char *selection, Option_t *option,Long64_t nentries, Long64_t firstentry)

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

TBranch* GetBranch(const char *name)

     Return pointer to the branch name in the current tree

Long64_t GetChainEntryNumber(Long64_t entry) const

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

Long64_t GetEntries() const

     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

Int_t GetEntry(Long64_t entry, Int_t getall)

     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
     o bytes read indicates a failure.

Int_t GetEntryWithIndex(Int_t major, Int_t minor)

     Return entry  corresponding to major and minor number
     For example:
         Int_t run   = 1234;
         Int_t event = 345;
         Long64_t serial= chain.GetEntryNumberWithIndex(run,event);
        now the variable serial is in the range [0,nentries] and one can do
        chain.GetEntry(serial);

     WARNING: This function will not work if teh chain has friend chains.

TFile* GetFile() const

      Return a pointer to the current file.
      if no file is connected, the first file is automatically loaded.

TLeaf* GetLeaf(const char *name)

      Return pointer to the leaf name in the current tree

TObjArray* GetListOfBranches()

     Return pointer to list of branches of current tree

TObjArray* GetListOfLeaves()

     Return pointer to list of leaves of current tree

Double_t GetMaximum(const char *columname)

     Return maximum of column with name columname

Double_t GetMinimum(const char *columname)

     Return minimum of column with name columname

Int_t GetNbranches()

     Return number of branches of current tree

const char* GetAlias(const char *aliasName) const

     Returns the expanded value of the alias.  Search in the friend if any

Double_t GetWeight() const

      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.

Int_t LoadBaskets(Long64_t /*maxmemory*/)

     This function overrides TTree::LoadBaskets and is dummy.
     It could be implemented and load all baskets of all trees in the chain.
     For the time being use TChain::Merge and TTree::LoadBasket
     on the resulting tree.

Long64_t LoadTree(Long64_t entry)

      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.

void Loop(Option_t *option, Long64_t nentries, Long64_t firstentry)

     Loop on nentries of this chain starting at firstentry

void ls(Option_t *option) const

Long64_t Merge(const char *name)

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

Long64_t Merge(TCollection * /* list */ )

     Merge all TChains in the list

Long64_t Merge(TFile *file, Int_t basketsize, Option_t *option)

         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.

      example using the file generated in $ROOTSYS/test/Event
      merge two copies of Event.root

            gSystem.Load("libEvent");
            TChain ch("T");
            ch.Add("Event1.root");
            ch.Add("Event2.root");
            ch.Merge("all.root");

     IMPORTANT Note 1: 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 2: The output file is automatically closed and deleted.
     This is required because in general the automatic file overflow described
     above may happen during the merge.
     If only the current file is produced (the file passed as first argument),
     one can instruct Merge to not close the file by specifying the option "keep".

     The function returns the total number of files produced.

void Print(Option_t *option) const

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

Long64_t Process(const char *filename,Option_t *option, Long64_t nentries, Long64_t firstentry)

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

Long64_t Process(TSelector *selector,Option_t *option, Long64_t nentries, Long64_t firstentry)

     Process this chain executing the code in selector

void Reset(Option_t *)

     Resets the definition of this chain

Long64_t Scan(const char *varexp, const char *selection, Option_t *option, Long64_t nentries, Long64_t firstentry)

     Loop on Tree 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

void SetAutoDelete(Bool_t autodelete)

      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.

void SetBranchAddress(const char *bname, void *add)

     Set branch address

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

     IMPORTANT REMARK:
     In case TChain::SetBranchStatus is called, it must be called
     BEFORE calling this function.

void SetBranchAddress(const char *bname,void *add, TClass *realClass, EDataType datatype, Bool_t ptr)

    Check if bname is already in the Status list
    Otherwise create a TChainElement object and set its address

void SetBranchStatus(const char *bname, Bool_t status, UInt_t *found)

     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
      See IMPORTANT REMARKS in TTree::SetBranchStatus and TChain::SetBranchAddress

      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.

void SetDirectory(TDirectory *dir)

     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.

void SetPacketSize(Int_t size)

     Set number of entries per packet for parallel root

void SetWeight(Double_t w, Option_t *option)

      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.

void Streamer(TBuffer &b)

     Stream a class object

void UseCache(Int_t maxCacheSize, Int_t pageSize)

     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.

void ReleaseChainProof()

     Removes the PROOF chain (if present).

void SetProof(TVirtualProof *proof)

     Sets the PROOF to be used for processing. "Draw" and "Processed" commands
     will be handled by the proof.
     If proof == (TVirtualProof*) -1 then the gProof is used.
     If proof == 0 no proof is connected and the previously connected
     proof is released.

Long64_t GetReadEntry() const

     See TTree::GetReadEntry().

TBranch* FindBranch(const char* branchname)

     See TTree::GetReadEntry().

TLeaf* FindLeaf(const char* searchname)

     See TTree::GetReadEntry()

Bool_t GetBranchStatus(const char *branchname) const

     See TTree::GetReadEntry()

### Inline Functions

                   void Draw(Option_t* opt)
                  Int_t Fill()
                  Int_t GetNtrees() const
             TObjArray* GetListOfFiles() const
                 TList* GetStatus() const
                 TTree* GetTree() const
                  Int_t GetTreeNumber() const
              Long64_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)

Author: Rene Brun 03/02/97
Last update: root/tree:$Name: $:$Id: TChain.cxx,v 1.110 2005/06/14 08:52:55 brun Exp $
Copyright (C) 1995-2000, Rene Brun and Fons Rademakers. *