Re: How to get an Histogram ?

Hi Jordi,

Your problem is that the histogram actually doesn't get overwritten in the subsequent calls. In your script, you first draw QCDnorm_corr_mu in histogram named "histo", and then you put the QCDnorm_corr_mu_btag into the SAME histogram. It's true, the contents is overwritten, but the histogram limits are not adjusted to the new variable. It doesn't happen if you wouldn't indicate the histogram name and use the default "htemp" which has the corresponding flag of resetting also the axis with the new data being filled.

In short - if you would try in your interactive test the following sequence:

root [1] HangingTree->Draw("QCDnorm_corr_mu>>histo")
root [2] histo->GetMean()
root [1] HangingTree->Draw("QCDnorm_corr_mu_btag>>histo")
root [2] histo->GetMean()

you would see the same results as your script produces. If you want CORRECT values for the mean, either use different names for the histograms, or take care to actually delete "histo" between fills.

Hope this helps,

        Eduard

 On Thu, 8 Sep 2011, Jordi Nadal wrote:

> Hi Suvayu,
>
> Thanks again for your time.
>
> I just ran your macro.
>
> [jnadal_at_at305 JetFitter]$ root test.C
>
> Welcome to the ATLAS rootlogon.C
> root [0]
> Processing test.C...
> Info in <TCanvas::MakeDefCanvas>: created default TCanvas with name c1
> QCDnorm_corr_mu -0.157223
> QCDnorm_corr_mu_btag 0.106851
> root [1] .q
> [jnadal_at_at305 JetFitter]$ root PSE/JO_muon_PSE_RbFree/sumRootFile.root
>
> Welcome to the ATLAS rootlogon.C
> root [0]
> Attaching file PSE/JO_muon_PSE_RbFree/sumRootFile.root as _file0...
> root [1] HangingTree->Draw("QCDnorm_corr_mu_btag>>histo")
> Info in <TCanvas::MakeDefCanvas>: created default TCanvas with name c1
> root [2] histo->GetMean()
> (const Double_t)1.69030729412928876e-01
> root [3]
>
> My problem is that I don't get the same number using the macro for variable (QCDnorm_corr_mu_btag) than looking at it in the root file.
>
> Thanks,
> Jordi
>
>
> On Sep 8, 2011, at 2:46 PM, suvayu ali wrote:
>
> > Hi Jordi,
> >
> > I am not sure about your issue as I don't know what exactly you are
> > trying to achieve. However after simplifying your example macro I
> > found two errors:
> >
> > {
> > int N = 2;
> > TString parnames[N] = { "QCDnorm_corr_mu", "QCDnorm_corr_mu_btag"};
> >
> >
> > TFile *file = TFile::Open("PSE/JO_muon_PSE_RbFree/sumRootFile.root");
> > TTree* HangingTree = (TTree*) file->Get("HangingTree");
> >
> > for(int i=0; i<N;i++){
> > TString raw = parnames[i];
> > // here the histograms get overwritten by subsequent calls to Draw()
> > HangingTree->Draw(raw+">>histo");
> > // this line does multiple declaration of h as the loop proceeds
> > // this is not correct C++ but might be forgivable in CINT, not sure
> > TH1D *h = (TH1D*) gROOT->FindObject("histo");
> > std::cout << raw << " " << h->GetMean() << std::endl;
> > }
> > }
> >
> > I hope this helps.
> >
> > --
> > Suvayu
> >
> > Open source is the future. It sets us free.
>
>
Received on Thu Sep 08 2011 - 16:43:16 CEST