Add histograms with slightly different bin inside a for loop

ROOT
1

I have a root file that consists of histograms of different bins, named histo1, histo2, histo3 and so on.
What I want to do is, add them so as to take the average of them.
The first problem is that to use Add() they should have the same bins. Is there a way to overcome this?

Secondly and more important at the moment, how can I loop over the histograms and access them by their name, since they have the same name, apart from an integer?

I was thinking something like

but I know that I cannot use a string as a histogram pointer. Is there a way around it?

2

Try: for (int i = min_i; i <= max_i; i++) { TH1 *h; SomeRootFile->GetObject(TString::Format("histo%d", i), h); if (!h) continue; // just a precaution ("histo..." not found) h->SomeHistogramFunction(); }

3

Thank you soooo much for your post!!!
This is working in general! For instance I could access some data and plot all of them on the same canvas.
However, when I try to add /sum(I want to take the avarage of the historgrams) them using

[code]void access(){

TFile *MyFile = new TFile(“FIMG1.root”,“READ”);
if ( MyFile->IsOpen() ) printf(“Root file opened successfully\n”);

TH1 *h;
TH1 *sum;

for (int i = 1; i <= 12; i++) {
//TH1 *h;
MyFile->GetObject(TString::Format(“FIMG1_EV_%d;1”, i), h);
if (!h) continue; // just a precaution (“histo…” not found)
h->Draw(“same”);//<----- This is working!!!
h->Add(TString::Format(“FIMG1_EV_%d;1”, i),1);//or h>Add(MyFile->GetObject(TString::Format(“FIMG1_EV_%d;1”, i), h),1);
}

}[/code]

I get the error

[quote](in TH1)
/usr/lib64/root/libHist.so -1:-1 0 public: virtual Bool_t TH1::Add(TF1* h1,Double_t c1=1,Option_t* option="");
/usr/lib64/root/libHist.so -1:-1 0 public: virtual Bool_t TH1::Add(const TH1* h1,Double_t c1=1);
/usr/lib64/root/libHist.so -1:-1 0 public: virtual Bool_t TH1::Add(const TH1* h,const TH1* h2,Double_t c1=1,Double_t c2=1); //MENU
*** Interpreter error recovered ***
[/quote]

P.S.: I am trying to find the documentation of GetObject but I cannot find it for TFile, only for TDirectory.

4

Try: [code]void access(void) {
TFile *MyFile = TFile::Open(“FIMG1.root”, “READ”);
if (!MyFile) return; // just a precaution (“MyFile” not found)

TH1 *sum = ((TH1 *)0);

for (int i = 1; i <= 12; i++) {
TH1 *h;
MyFile->GetObject(TString::Format(“FIMG1_EV_%d;1”, i), h);
if (!h) continue; // just a precaution (“histo…” not found)
if (sum) sum->Add(h); else sum = h;
}

if (sum) sum->Scale((1./12.)); // "average"
if (sum) sum->Draw();
}[/code]
BTW. TFile inherits from TDirectoryFile which inherits from TDirectory which inherits from TNamed which inherits from TObject.

5

Thank you once again!!!
The problem now is that the histogram don’t have the same number of bins, which was expected…

Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Error in <TH1F::Add>: Attempt to add histograms with different number of bins Info in <TCanvas::MakeDefCanvas>: created default TCanvas with name c1

Is there a way to overcome this and sum all the histograms, so as to calculate the mean value?
I think that I must use GetBinContent() and SetBinContent() but I really don’t know how to set this up…:frowning: