Colin,
The following few lines are extracted from the TH1 documentation at
http://root.cern.ch/root/html/TH1.html
*-* Convention for numbering bins
*-* =============================
*-* For all histogram types: nbins, xlow, xup
*-* bin = 0; underflow bin
*-* bin = 1; first bin with low-edge xlow INCLUDED
*-* bin = nbins; last bin with upper-edge xup EXCLUDED
*-* bin = nbins+1; overflow bin
*-*
In the case of 2-d and 3-d histograms (and consistent with 1-d
histograms)
you can do :
int globalbin = h->GetBin(binx,biny) ; // for a 2-d
int globalbin = h->GetBin(binx,biny,binz); // for a 3-d
In case of 1-d
int globalbin = h->GetBin(binx) = binx
You can then access the bin contents, errors, etc with
h->GetBinContent(globalbin);
globalbin is a linearized bin number in one-dim structure.
Rene Brun
C. Bernet wrote:
>
> Hi,
>
> It looks like when you create a 2d histogram hist, bins in x and y start
> at 1.
> When you execute the following command :
>
> hist->GetBin(1,1)
>
> the result is not 1 (0 would also be ok) but 19 in my case (TH2F, 16*16
> bins).
>
> Yet :
> hist->GetBin(0,0) gives 0. But if you try to fill this bin
> (hist->SetBinContent(0,1.)) and draw the TH2F, you see that this bin is
> out of range....
>
> Does anybody know if it's a bug or if the previous bins are used for
> something else ?
>
> Thanks a lot.
> Colin
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