Can SetBinContent change the number of binn?!

ROOT
1

Hi rooters,
I am observing an extremely strange thing. Can SetBinContent change the number of bins?

This is the code I have

    cout<<h->GetNbinsX()<<endl;
    h->SetBinContent(h->GetNbinsX()+ 1, scale);
    cout << "Finish Lumi normalizing histogram.\n";
    cout<<h->GetNbinsX()<<endl;

and this is the output

18
Finish Lumi normalizing histogram.
36

2

Try:
h->ResetBit(TH1::kCanRebin);

3

Hi ,
Where should I add this piece of code?
TH1::kCanRebin is not defined in root!

Cheers

4

It exists in ROOT 5 (In compiled code #include “TH1.h”).
It seems that some genius removed it in ROOT 6 :mrgreen:
So, in ROOT 6, try (in compiled code #include “TAxis.h”):
h->GetXaxis()->SetCanExtend(kFALSE);

5

Yes, it is written here.

6

thanks a lot,
I tried it and it works. However, I still do not fundamentally understand why the number of bins would change when I call SetBinContent() function.
I only want to set the content of the overflow bin!

Cheers

7

Hi
if you dont like the way it is implemented you may exploit
the inheritance of say TH1F from TArrayF:

TH1F h("zz", "yy", 10,0,10);
h[2] = 2;   // bin 2
h[0] = 34;  // underflow
h[11] = 26; // overflow
h[12] = 34;
Error in <TArrayF::operator[]>: index 12 out of bounds...

Otto

8

Just be aware that TH1F::SetBinContent automatically performs some [url=https://root-forum.cern.ch/t/bin-errors-with-addbincontent-and-sumw2/19465/5 side actions[/url] (which are not done if you go via the TArrayF shortcut).
In any case, after you manually modify bin contents, I think you should call TH1::ResetStats.