ROOT_528-00b_version: tutorials/tree/copytree3.C Source File

00001 void copytree3() {
00002 // Example of Root macro to copy a subset of a Tree to a new Tree
00003 // Only selected entries are copied to the new Tree.
00004 // The input file has been generated by the program in $ROOTSYS/test/Event
00005 // with   Event 1000 1 99 1
00006 //Author: Rene Brun
00007    
00008    gSystem->Load("$ROOTSYS/test/libEvent");
00009 
00010    //Get old file, old tree and set top branch address
00011    TFile *oldfile = new TFile("$ROOTSYS/test/Event.root");
00012    TTree *oldtree = (TTree*)oldfile->Get("T");
00013    Int_t nentries = (Int_t)oldtree->GetEntries();
00014    Event *event   = 0;
00015    oldtree->SetBranchAddress("event",&event);
00016 
00017    //Create a new file + a clone of old tree in new file
00018    TFile *newfile = new TFile("small.root","recreate");
00019    TTree *newtree = oldtree->CloneTree(0);
00020 
00021    for (Int_t i=0;i<nentries; i++) {
00022       oldtree->GetEntry(i);
00023       if (event->GetNtrack() > 605) newtree->Fill();
00024       event->Clear();
00025    }
00026    newtree->Print();
00027    newtree->AutoSave();
00028    delete oldfile;
00029    delete newfile;
00030 }