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Reference Guide
copytree.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
5 ///
6 /// The input file has been generated by the program in `$ROOTSYS/test/Event`
7 /// with `Event 1000 1 1 1`.
8 ///
9 /// \macro_code
10 ///
11 /// \author Rene Brun
12 
13 // Load the library at macro parsing time: we need this to use its content in the code
14 R__LOAD_LIBRARY($ROOTSYS/test/libEvent.so)
15 
16 void copytree()
17 {
18 
19  TString dir = "$ROOTSYS/test/Event.root";
20  gSystem->ExpandPathName(dir);
21  const auto filename = gSystem->AccessPathName(dir) ? "./Event.root" : "$ROOTSYS/test/Event.root";
22 
23  TFile oldfile(filename);
24  TTree *oldtree;
25  oldfile.GetObject("T", oldtree);
26 
27  // Deactivate all branches
28  oldtree->SetBranchStatus("*", 0);
29 
30  // Activate only four of them
31  for (auto activeBranchName : {"event", "fNtrack", "fNseg", "fH"})
32  oldtree->SetBranchStatus(activeBranchName, 1);
33 
34  // Create a new file + a clone of old tree in new file
35  TFile newfile("small.root", "recreate");
36  auto newtree = oldtree->CloneTree();
37 
38  newtree->Print();
39  newfile.Write();
40 }
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
virtual void Print(Option_t *option="") const
Print a summary of the tree contents.
Definition: TTree.cxx:6996
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
R__EXTERN TSystem * gSystem
Definition: TSystem.h:557
#define R__LOAD_LIBRARY(LIBRARY)
Definition: Rtypes.h:473
typedef void((*Func_t)())
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