Re: [ROOT] TTreeFormula within TSelector::ProcessCut

From: Rene Brun (Rene.Brun@cern.ch)
Date: Fri Dec 21 2001 - 08:55:56 MET


Hi Chris,

I do not think that it is a good idea to use TTreeFormula within a TSelector.
If you already have a TSelector derived class, you should implement
the function MySelector::ProcessCut. In this function, you should call
the TBranch::GetEntry (not TTree::GetEntry) in the order where you eliminate
as many candidates as possible and minimizing the I/O.
You can see an example in $ROOTSYS/tutorials/h1analysis.C

Use TBranch::GetEntry as shown in this example instead of the mechanism
via TTree::SetBranchStatus. The pointers to the branches are already declared
and precomputed for you in mySelector.h

Rene Brun


Chris Roat wrote:
> 
> Hi Philipe,
> 
> Thanks so much for your solution.  It worked great and I'm now back up and
> running.  I have another question on a related note.
> 
> I need to be sure that my TSelector reads in the branches necessary (and
> *only* those branches, since I have 100s) for the TTreeFormulas I am
> using.  But I don't see the need to add/change SetBranchStatus lines in my
> TSelector::Init method everytime I add/change my TTreeFormulas.
> 
> Is there a way to do this more easily, like by looping over the leaves a
> TTreeFormula needs?
> 
> Cheers,
> Chris
> 
> *** Today, you (Philippe Canal) wrote ***
> 
> >Hi Chris,
> >
> >The problem was that the TTreeFormula were not informed properly that
> >the chain loaded a need TTree.  To fix that you need to add at the end of
> >generic::Notify the following:
> >
> >  // fChain->LoadTree(fChain->GetReadEntry());
> >  // Also update the formulas:
> >  for (Int_t cut=0; cut<_cs->nCuts(); cut++) {
> >     ttform[cut]->UpdateFormulaLeaves();
> >  }
> >
> >Now in your sample case (only one file), it should not have been loading
> >any new file in the first place.  The reason why it was, is that you have
> >in all your selector's Notify method (like generic::Notify) calls like:
> >
> >       fChain->SetBranchStatus("*",kFALSE);
> >
> >This forces a reload of the current file.  The SetBranchStatus actually
> >belongs in the generic::Init method because they only need to be once
> >by chain.  The chain (at least in newer ROOT) keeps track of the
> >info and pass it to each TTree.  If for some reasons (very old ROOT
> >version) this does not work, then uncomment the first like in my
> >first code fragment.
> >
> >Cheers,
> >Philipe.
> >
> >
> >-----Original Message-----
> >From: owner-roottalk@pcroot.cern.ch
> >[mailto:owner-roottalk@pcroot.cern.ch]On Behalf Of Chris Roat
> >Sent: Wednesday, December 19, 2001 1:03 PM
> >To: roottalk@pcroot.cern.ch
> >Subject: [ROOT] TTreeFormula within TSelector::ProcessCut
> >
> >
> >Hi ROOT,
> >
> >I'm having problems finding out if a particular entry in a tree passes a
> >cut.  I'm using a TSelector which takes recieves a list of strings (which
> >are cuts, of the form "p>3" or "myBool" from the outside world).  During
> >ProcessCut/ProcessFill, I would like to see if the entry I'm on passes any
> >of the strings.
> >
> >I am trying to use TTreeFormula to tackle this, but without prolonged
> >luck.  It works fine on the first entry - EvalInstance(0) returns the
> >correct answer, so I'm on the right track.  However, EvalInstance(0) seg
> >faults on subsequent entries.
> >
> >Could there be a problem with ProcessCut() and EvalInstance() both getting
> >info from the tree?
> >
> >Thanks for any insight,
> >Chris
> >
> >
> >



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