tree111_copy.C

Go to the documentation of this file.

/// \file
/// \ingroup tutorial_tree
/// \notebook -nodraw
/// Copy a subset of a Tree to a new Tree, one branch in a separate file.
///
/// One branch of the new Tree is written to a separate file
/// The input file has been generated by the program in `$ROOTSYS/test/Event`
/// with the command `Event 1000 1 1 1`
///
/// \macro_code
///
/// \author Rene Brun
 
#ifdef ACTUAL_RUN  // -------- Second pass: dictionary already built --------
 
#include "./Event.h"  // now safe to include Event, its dictionary is loaded
 
void run()
{
   TFile oldfile("tree108.root");
   TTree *oldtree;
   oldfile.GetObject("t4", oldtree);
 
   // Activate only four of them
   for (auto activeBranchName : {"event_split", "fNtrack", "fNseg", "fH"}) {
      oldtree->SetBranchStatus(activeBranchName, 1);
   }
 
   // Create a new file + a clone of old tree header. Do not copy events
   TFile newfile("tree111.root", "recreate");
   auto newtree = oldtree->CloneTree(0);
 
   // Divert branch fH to a separate file and copy all events
   newtree->GetBranch("fH")->SetFile("small_fH.root");
   newtree->CopyEntries(oldtree);
 
   newtree->Print();
   newfile.Write();
}
 
#else  // -------- First pass: build dictionary + rerun macro --------
 
void tree111_copy()
{
   TString tutdir = gROOT->GetTutorialDir();
   gROOT->ProcessLine(".L " + tutdir + "/io/tree/Event.cxx+");
   gROOT->ProcessLine("#define ACTUAL_RUN yes");
   gROOT->ProcessLine("#include \"" __FILE__ "\"");
   gROOT->ProcessLine("run()");
}
 
#endif