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Reference Guide
copytree2.C
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1 /// \file
2 /// \ingroup tutorial_tree
3 /// \notebook -nodraw
4 /// Copy a subset of a Tree to a new Tree, one branch in a separate file.
5 ///
6 /// One branch of the new Tree is written to a separate file
7 /// The input file has been generated by the program in `$ROOTSYS/test/Event`
8 /// with the command `Event 1000 1 1 1`
9 ///
10 /// \macro_code
11 ///
12 /// \author Rene Brun
13 
14 // Load the library at macro parsing time: we need this to use its content in the code
15 R__LOAD_LIBRARY($ROOTSYS/test/libEvent.so)
16 
17 void copytree2()
18 {
19 
20  TString dir = "$ROOTSYS/test/Event.root";
21  gSystem->ExpandPathName(dir);
22  const auto filename = gSystem->AccessPathName(dir) ? "./Event.root" : "$ROOTSYS/test/Event.root";
23 
24  TFile oldfile(filename);
25  TTree *oldtree;
26  oldfile.GetObject("T", oldtree);
27 
28  // Activate only four of them
29  for (auto activeBranchName : {"event", "fNtrack", "fNseg", "fH"}) {
30  oldtree->SetBranchStatus(activeBranchName, 1);
31  }
32 
33  // Create a new file + a clone of old tree header. Do not copy events
34  TFile newfile("small.root", "recreate");
35  auto newtree = oldtree->CloneTree(0);
36 
37  // Divert branch fH to a separate file and copy all events
38  newtree->GetBranch("fH")->SetFile("small_fH.root");
39  newtree->CopyEntries(oldtree);
40 
41  newtree->Print();
42  newfile.Write();
43 }
virtual Bool_t AccessPathName(const char *path, EAccessMode mode=kFileExists)
Returns FALSE if one can access a file using the specified access mode.
Definition: TSystem.cxx:1279
virtual void SetBranchStatus(const char *bname, Bool_t status=1, UInt_t *found=0)
Set branch status to Process or DoNotProcess.
Definition: TTree.cxx:8216
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format...
Definition: TFile.h:48
Definition: test.py:1
Basic string class.
Definition: TString.h:131
virtual TTree * CloneTree(Long64_t nentries=-1, Option_t *option="")
Create a clone of this tree and copy nentries.
Definition: TTree.cxx:3037
virtual TBranch * GetBranch(const char *name)
Return pointer to the branch with the given name in this tree or its friends.
Definition: TTree.cxx:5096
R__EXTERN TSystem * gSystem
Definition: TSystem.h:557
#define R__LOAD_LIBRARY(LIBRARY)
Definition: Rtypes.h:473
typedef void((*Func_t)())
virtual void SetFile(TFile *file=0)
Set file where this branch writes/reads its buffers.
Definition: TBranch.cxx:2677
A TTree represents a columnar dataset.
Definition: TTree.h:72
virtual Bool_t ExpandPathName(TString &path)
Expand a pathname getting rid of special shell characters like ~.
Definition: TSystem.cxx:1257