Re: Problem reading TClonesArray from TTrees

From: Axel Naumann <Axel.Naumann_at_cern.ch>
Date: Tue, 24 Nov 2009 09:59:51 +0100

Hi Suvayu,

*first* load the TTree's entry, *then* access its data, not the other way around :-)

Cheers, Axel.

Suvayu Ali wrote on 11/24/2009 08:30 AM:
> Hi everyone,
>
> I think I am missing some extremely simple step, but I can't figure this
> one out. :(
>
> I am creating some TLorentzVectors from a flat ntuple and saving them in
> a TTree using TClonesArray using a class originally created by
> TTree::MakeClass(). I have only edited the Loop() method. This is how I
> am attempting it.
>

>> TFile fout("ttbar-dil.root","recreate");
>> TTree *fEventsTree = new TTree("EventCollection", "Zprime-->ttbar");
>> TClonesArray jetsLV("TLorentzVector", 2);
>> TClonesArray lepLV("TLorentzVector", 2);
>> TClonesArray metLV("TLorentzVector", 2);
>> ...
>> fEventsTree->Branch( "Jets", &jetsLV);
>> fEventsTree->Branch( "Leptons", &lepLV);
>> fEventsTree->Branch( "MET", &metLV);
>> ...
>> // code to implement cuts and fill the Tree,
>> ...
>> fout.Write();
>> fout.Close();

>
> Then I try to access it like this from my analysis macro.
>

>> TFile *fin1 = new TFile("ttbar-dil.root", "read");
>> TTree *fEvents1 = (TTree*) fin1->Get("EventCollection");
>> TClonesArray *jetsLV1 = new TClonesArray("TLorentzVector");
>> TClonesArray *lepLV1 = new TClonesArray("TLorentzVector");
>> ...
>> fEvents1->SetBranchAddress("Jets", &jetsLV1);
>> fEvents1->SetBranchAddress("Leptons", &lepLV1);

>
> But the following always gives me zero.
>

>>  Int_t njets = jetsLV1->GetEntriesFast();
>>  Int_t nlep = lepLV1->GetEntriesFast();

>
> Now using a TBrowser from the ROOT interactive prompt I can see the Tree
> is not empty. I can even plot any quantity I want to and get histograms
> showing me the events are there exactly as I would expect it to be!
> Where am I going wrong?
>
> I have attached my analysis macro. Since the list guidelines say large
> attachments are not welcome, I have put one of my small TTrees on a
> webpage @ http://hep.phys.sfu.ca/~suvayu/TTree-prob/
>
> Thank you for any help on this.
>
> ROOT version:
> F11: ROOT 5.25/03 (trunk_at_30937, Oct 31 2009, 21:58:43 on linuxx8664gcc)
> Ubuntu 9.04: ROOT 5.25/01 (trunk_at_30039, Sep 04 2009, 13:39:06 on linux)
>
Received on Tue Nov 24 2009 - 09:57:51 CET