Re: [ROOT] using TEventLists to copy tree entries?

From: Rene Brun (Rene.Brun@cern.ch)
Date: Fri Aug 10 2001 - 08:50:10 MEST 

Hi Richard,

Yes, this is possible. Example:

void makeList() {
   TFile *f1 = new TFile("hsimple.root");
   TTree *ntuple = (TTree*) f1->Get("ntuple");
   ntuple->Draw(">>elist","py>2");
   TEventList *elist = (TEventList*)gDirectory->Get("elist");
   TFile ef("elist.root","recreate");                       
   elist.Write();
}

void makeSmall() {
   TFile *f = new TFile("elist.root");
   TEventList *elist = (TEventList*)f->Get("elist");
   TFile *f1 = new TFile("hsimple.root");
   TTree *ntuple = (TTree*) f1->Get("ntuple");
   ntuple->SetEventList(elist);
   TFile *f2 = new TFile("small.root","recreate");
   TTree *small = ntuple->CopyTree("");
   small->Write();
   small->Print();
}


Rene Brun

Dubois, Richard wrote:
> 
> Is it possible to use event lists to selectively grab entries in a tree/file and copy them to a new file? Something like
> 
>  create event list from old tree, do oldtree->SetEventList
> 
>  then clone/copy entries to a new tree, but only the ones specified in the event list? I tried just that from the copytree example in the tutorials, but got a full copy of oldtree...
> 
>  The basic idea is that we have 400 MB of files, we want to select out about 25 MB and simply create a new file with just the 25 MB.
> 
> Thanks,
> 
> Richard
> --
> Richard Dubois
> Stanford Linear Accelerator Center
> 650-926-3824
> 650-926-8616 (FAX)
> richard@slac.stanford.edu
> http://www.slac.stanford.edu/~richard

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