copytree.C File Reference

Detailed Description

Copy a subset of a Tree to a new Tree

The input file has been generated by the program in $ROOTSYS/test/Event with Event 1000 1 1 1.

 
// Load the library at macro parsing time: we need this to use its content in the code
R__LOAD_LIBRARY($ROOTSYS/test/libEvent.so)
 
void copytree()
{
 
   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);
 
   // Deactivate all branches
   oldtree->SetBranchStatus("*", 0);
 
   // Activate only four of them
   for (auto activeBranchName : {"event", "fNtrack", "fNseg", "fH"})
      oldtree->SetBranchStatus(activeBranchName, 1);
 
   // Create a new file + a clone of old tree in new file
   TFile newfile("small.root", "recreate");
   auto newtree = oldtree->CloneTree();
 
   newtree->Print();
   newfile.Write();
}

Author

Rene Brun

Definition in file copytree.C.