Re: [ROOT] Drawing multiple times to same temp histogram

From: Rene Brun (Rene.Brun@cern.ch)
Date: Wed Mar 27 2002 - 17:16:54 MET


Vuko,

Sorry if I was not clear enough in my previous mail. I suggest to replace:
   int ilay;
   for (ilay=0; ilay<4; ilay++) {
     t1->Draw(scalerName(ilay+1)+":time >> srhist",cutString);
     srhistos[ilay]= new TH2F(*srhist);  
by
   int ilay;
   TString hname = "rhist_";
   for (ilay=0; ilay<4; ilay++) {
     t1->Draw(scalerName(ilay+1)+":time >> srhist",cutString);
     srhistos[ilay]= (TH2F*)srhist->Clone(hname+ilay);

Rene Brun

     
Vuko Brigljevic wrote:
> 
> Hi Rene,
> 
> Thanks for helping!
> 
> Rene Brun wrote:
> >
> > Hi Vuko,
> >
> > Give a different name to each of your histograms.
> 
> To which histogram should I give a different name, to the one named
> "srhist" (see my code below in my 1st message) to which I am copying the
> output of Tree->Draw? But then I can't use a loop, but that would be
> rather
> annoying. I am probably misunderstanding...
> 
> > In your case, t1->Draw will delete the previous histogram named "srhist"
> > and your pointers in srhistos[] will be dangling pointers.
> 
> Really? I am confused, I would have thought that the line:
> 
>      srhistos[ilay]= new TH2F(*srhist);
> 
> creates a new TH2F (srhistos is an array of pointers to TH2F
> objects) using the copy constructor, i.e. *(srhistos[ilay])
> is a COPY of *srhist, and not the same object, or does the copy
> constructor just let some parts of TH2F point to the original
> one? If the latter is the case, that does not seem to be the point
> of a copy constructor IMHO.
> 
> Can you please clarify this, thanks.
> 
> Vuko
> 
> > On Tue, 26 Mar 2002, Vuko Brigljevic wrote:
> >
> > > Hi all,
> > >
> > > The following is done using root 3.02/07 on SunOS,
> > > I see the same problem on Linux.
> > >
> > > I am trying to use the same 2D histo several times in a row
> > > as output of a Tree->Draw() and I am crashing. The code:
> > >
> > >
> > >   TH2F *srhistos[10];
> > >
> > >   int ilay;
> > >   for (ilay=0; ilay<4; ilay++) {
> > >     t1->Draw(scalerName(ilay+1)+":time >> srhist",cutString);
> > >     srhistos[ilay]= new TH2F(*srhist);
> > >     srhistos[ilay]->GetXaxis()->SetTimeDisplay(1);
> > >     srhistos[ilay]->GetXaxis()->SetTimeFormat("%d/%m");
> > >     srhistos[ilay]->Draw();
> > >     gPad->SaveAs(TString(prefix+"singles-layer"+ilay+".eps"));
> > >     //    srhist.Reset();     tried this as well: does not help
> > >     delete srhist;
> > >   }
> > >
> > > Whether I am deleting the temporary histogram (srhist),
> > > resetting it or doing neither of both, I am always
> > > crashing with the following output:
> > >
> > > Info in <TPad::Print>: PostScript file lastDays/singles-layer1.eps has
> > > been created
> > >
> > >  *** Break *** segmentation violation
> > > Root > Function makePlots() busy flag cleared
> > > Function doPlots() busy flag cleared
> > >
> > > How am I supposed to do something like that?
> > >
> > > Thanks for any help!
> > >
> > > Vuko
> > >
> > >
> > > ========================================================================
> > >  Vuko Brigljevic                        | Mail : SLAC, Mail Stop 41
> > >  Lawrence Livermore National Laboratory |        P.O. Box 4349, Stanford
> > >  Nuclear and Particle Physics Division  |        CA 94309, USA
> > >                                         | SLAC-Office : B280- room 143
> > >  Member of the BaBar Collaboration      | Phone : +1-650-926 8512
> > >  <vuko@slac.stanford.edu>          <http://www.slac.stanford.edu/~vuko>
> > > ========================================================================
> > >
> 
> --
> 
> ========================================================================
>  Vuko Brigljevic                        | Mail : SLAC, Mail Stop 41
>  Lawrence Livermore National Laboratory |        P.O. Box 4349, Stanford
>  Nuclear and Particle Physics Division  |        CA 94309, USA
>                                         | SLAC-Office : B280- room 143
>  Member of the BaBar Collaboration      | Phone : +1-650-926 8512
>  <vuko@slac.stanford.edu>          <http://www.slac.stanford.edu/~vuko>
> ========================================================================



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