Re: How to get an Histogram ?

From: Eduard Avetisyan <Eduard.Avetisyan_at_desy.de>
Date: Thu, 8 Sep 2011 20:12:06 +0200

Hello Jordi,

On Thu, 8 Sep 2011, Jordi Nadal wrote:

> Hello Eduard,
>
> I think you are complete right.
>
> A delete histo; directly fails… so I am trying to set a different histo each iteration.

Well you don't have a variable called "histo" in your script. To delete the object you should use the modified script like here:

>>> // this is not correct C++ but might be forgivable in CINT, not sure /* here goes the new histogram object */

      TH1D *h;
      if (h) delete h;

>>> h = (TH1D*) gROOT->FindObject("histo");

or, as another alternative, you may force recreating the histogram by specifying it's boundaries at the TTree::Draw() phase:

> >>> HangingTree->Draw(raw+">>histo(100,0.,10.)");
this will effectively reset the histogram AND it's axis, but indeed this time you will have the same boundaries for both variables.

Have fun

        Eduard

>
> Thanks all again.
>
> Cheers,
> JOrdi
>
>
> On Sep 8, 2011, at 4:43 PM, Eduard Avetisyan wrote:
>
> >
> >
> > 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 - 20:12:17 CEST