copytree3.C File Reference

Detailed Description

Example of Root macro to copy a subset of a Tree to a new Tree, selecting entries.

Only selected entries are copied to the new Tree. The input file has been generated by the program in $ROOTSYS/test/Event with Event 1000 1 99 1

 
R__LOAD_LIBRARY($ROOTSYS/test/libEvent.so)
 
void copytree3()
{
   // Get old file, old tree and set top branch address
   TString dir = "$ROOTSYS/test/Event.root";
   gSystem->ExpandPathName(dir);
   const auto filename = gSystem->AccessPathName(dir) ? "./Event.root" : "$ROOTSYS/test/Event.root";
 
   TFile oldfile(filename);
   TTree *oldtree;
   oldfile.GetObject("T", oldtree);
 
   const auto nentries = oldtree->GetEntries();
 
   Event *event = nullptr;
   oldtree->SetBranchAddress("event", &event);
 
   // Create a new file + a clone of old tree in new file
   TFile newfile("small.root", "recreate");
   auto newtree = oldtree->CloneTree(0);
 
   for (auto i : ROOT::TSeqI(nentries)) {
      oldtree->GetEntry(i);
      if (event->GetNtrack() > 605)
         newtree->Fill();
      event->Clear();
   }
 
   newtree->Print();
   newfile.Write();
}

Author

Rene Brun

Definition in file copytree3.C.