Re: How to get the histogram in a pad ?

Rene Brun (Rene.Brun@cern.ch)
Fri, 23 Apr 1999 15:32:37 +0000

Hi Damir,
If I understand correctly your question, you want to do something like
"You are going downtown, looking for a nice girl.
You do not know her name
You do not know where she is
The only thing you can do is to be meet with the first nice girl !"

Translated in Root format, this gives:
"you have a directory containing objects, including histograms 1-d,
2-d, etc
"you want to get say the first object deriving from TH1"

If the answer is yes, you can use the following loop:

TIter next(gDirectory->GetList());
TObject *obj;
while ((obj = next())) {
if (obj->InheritsFrom("TH1")) {
return obj; // have found an histogram, return the pointer
}
}

Rene Brun

Damir Buskulic wrote:
>
> Hi all,
>
> Probably a stupid question that has been answered many times but I can't
> seem to find it in roottalk
>
> Suppose I have an histogram in a pad, without knowing it's name or
> having a pointer to it. How can I get a pointer to it ? I tried various
> things such as :
>
> * gPad->GetListOfPrimitives()->FindObject(...) need the name or a
> pointer to the object, I don't have it
> * loop on the list of primitives and try to compare with the
> obj.Class()->Compare(known_histo) but all objects are put in the list as
> TObjects, so one doesn't know if they are TH1F's or not...
>
> All in all, one always needs the name or pointer to the histo. Looping
> on the list of histograms found in gDirectory is not very handy,
> especially if one has histograms outside a directory.
> Well, it should be simple...
>
> Cheers
>
> Damir
>
> --
> =====================================================================
> | Damir Buskulic | Universite de Savoie/LAPP |
> | | Chemin de Bellevue, B.P. 110 |
> | Tel : +33 (0)450091600 | F-74941 Annecy-le-Vieux Cedex |
> | e-mail: buskulic@lapp.in2p3.fr | FRANCE |
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