Plotting Multiple Histograms with Same Title

ROOT
1

Hello,

I am trying to plot multiple (~20) histograms with the same name, from the same .root file, onto one plot.

In my case, I have .root file, with ~20 histograms, each of the same name (myhist;1 myhist;2 myhist;3…)
and all the same title (myhist).

Here is [some parts pseudo-]code of what I am doing:

TFile *f=new TFile("myfile.root");
TCanvas *c1=new TCanvas("c1","c1",800,800);

bool setupComplete(false);
  
for (int i(1);i<=20;++i){

    TH1F* h;
    h = (TH1F*) f->Get("myhist;i"); //pseudocode, I call a little function which returns the char* properly e.g. "myhist;1"

    if (!h){
      std::cout<<"Error: histogram not found"<<std::endl;
      continue;
    }

    if (!setupComplete) { h->Draw(); setupComplete=true; }
    else h->Draw("SAME");
  }

So I want to draw all of these histograms on the same plot, adding one at a time. All the histograms have the same # of entries, same binning, same boundaries. What I get back I have attached as canvas.png, obviously not what I was going for.

I have tried similar loops where the histograms all have different names (myhist1;1 myhist2;1 myhist3;1) and that seems to work fine, so I think the problem is with the shared name.

I can also print out info from the histogram, statistical quantities like the mean, etc., so it appears to be reading the histograms from the file perfectly fine.

If I print out the value of h (the address in memory), it is always the same for all the histograms. I am not sure how to interpret this…

Any help would be greatly appreciated. Thank you.

canvas.png678×600 11.5 KB

2

The problem is NOT the same “title” but it’s the same “name” of all histograms (the number after the “;” is the so called “cycle”).
Try with “f->FindObjectAny” instead of “f->Get”.
See [url]Problem with Reading Root File and [url]Problem with Reading Root File and [url]Aux;1 aux;2 aux3;
P.S. Of course, the preferred solution is to create / store histograms with distinct “names”, and then use “GetObject” to “retrieve” them as described in http://root.cern.ch/root/html/TDirectoryFile.html#TDirectoryFile:Get
BTW. The “pseudocode” can be as simple as … TString::Format(“myhist;%d”, i)

3

Thanks, those solutions work perfectly.

(and I made sure I used ‘name’ all through the post, but forgot to fix the ‘title’ in the subject)