Stephen Bailey wrote:
>
> Hi.
>
> I'm trying to project an ntuple into a histogram which I
> defined so that I can control the number of bins used.
> e.g.
>
> TH1F h1 = new TH1F("blat", "quat", 20, 4.5, 6);
> ntuple->Draw("m>>+h1", "(4.5<m)&&(m<6.0)");
> h1->Draw();
>
> I also tryed m>>h1, but the ntuple->Draw command always
> picks its own choice for number of bins and h1 always
> seems to remain empty. If I don't predefine h1 then it
> gets created and properly filled but I don't have control
> over the number of bins.
>
> Is there a way to do this easily (i.e. without looping
> trough the ntuple and filling the histogram event by event)?
>
Replace:
TH1F h1 = new TH1F(..
by
TH1F *h1 = new TH1F(..
The TTree::Draw function (in the form "m>>+h1") fills an histogram
with the name "h1". In your case h1 is the name of the pointer,
not the name of the histogram ("blat").
It is a good practice to have the pointer_name = histogram_name.
Your program will work with:
TH1F *h1 = new TH1F("blat", "quat", 20, 4.5, 6);
ntuple->Draw("m>>+blat", "(4.5<m)&&(m<6.0)");
h1->Draw();
or
TH1F *blat = new TH1F("blat", "quat", 20, 4.5, 6);
ntuple->Draw("m>>+blat", "(4.5<m)&&(m<6.0)");
blat->Draw();
Rene Brun
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