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copytree3.C
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1 /// \file
2 /// \ingroup tutorial_tree
3 /// \notebook -nodraw
4 /// Example of Root macro to copy a subset of a Tree to a new Tree, selecting entries.
5 ///
6 /// Only selected entries are copied to the new Tree.
7 /// The input file has been generated by the program in `$ROOTSYS/test/Event`
8 /// with `Event 1000 1 99 1`
9 ///
10 /// \macro_code
11 ///
12 /// \author Rene Brun
13 
14 R__LOAD_LIBRARY($ROOTSYS/test/libEvent.so)
15 
16 void copytree3()
17 {
18  // Get old file, old tree and set top branch address
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  const auto nentries = oldtree->GetEntries();
28 
29  Event *event = nullptr;
30  oldtree->SetBranchAddress("event", &event);
31 
32  // Create a new file + a clone of old tree in new file
33  TFile newfile("small.root", "recreate");
34  auto newtree = oldtree->CloneTree(0);
35 
36  for (auto i : ROOT::TSeqI(nentries)) {
37  oldtree->GetEntry(i);
38  if (event->GetNtrack() > 605)
39  newtree->Fill();
40  event->Clear();
41  }
42 
43  newtree->Print();
44  newfile.Write();
45 }
TTree::CloneTree
virtual TTree * CloneTree(Long64_t nentries=-1, Option_t *option="")
Create a clone of this tree and copy nentries.
Definition: TTree.cxx:3089
TTree
A TTree represents a columnar dataset.
Definition: TTree.h:79
TTree::SetBranchAddress
virtual Int_t SetBranchAddress(const char *bname, void *add, TBranch **ptr=0)
Change branch address, dealing with clone trees properly.
Definition: TTree.cxx:8210
nentries
int nentries
Definition: THbookFile.cxx:91
TString
Basic string class.
Definition: TString.h:136
TSystem::AccessPathName
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:1294
test
Definition: test.py:1
TTree::GetEntry
virtual Int_t GetEntry(Long64_t entry=0, Int_t getall=0)
Read all branches of entry and return total number of bytes read.
Definition: TTree.cxx:5537
TSystem::ExpandPathName
virtual Bool_t ExpandPathName(TString &path)
Expand a pathname getting rid of special shell characters like ~.
Definition: TSystem.cxx:1272
void
typedef void((*Func_t)())
TFile
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format.
Definition: TFile.h:54
gSystem
R__EXTERN TSystem * gSystem
Definition: TSystem.h:559
ROOT::TSeq
A pseudo container class which is a generator of indices.
Definition: TSeq.hxx:66
TTree::GetEntries
virtual Long64_t GetEntries() const
Definition: TTree.h:458
R__LOAD_LIBRARY
#define R__LOAD_LIBRARY(LIBRARY)
Definition: Rtypes.h:472