Re: [ROOT] Ntuple projection.

From: Rene Brun (Rene.Brun@cern.ch)
Date: Mon Jun 07 2004 - 08:17:42 MEST


Hi Zhou,

When you use the form:
  
n1->Draw("Y:X>>ha2"

the histogram ha2 is assumed to be accessible in the current directory.
In your case, simply do:

TFile f1("tmp_proton.root");
TNtuple *n1=(TNtuple*)f1.Get("h9");
TH2F *ha2 =new TH2F("ha2","ADC",200,-100.,100.,200,-100.,100.);
n1->Draw("Y:X>>ha2","","scat");

Note that you can also use the form:
n1->Draw("Y:X>>ha2(200,-100,100,200,-100,100);
see documentation of TTree::Draw

Rene Brun

Zhou SuiJian wrote:
> 
> Dear All,
>   Can anybody help me to solve the problem?
> I want to project two of the variables in a
> Ntuple into a TH2F, which has a predefined
> range for both X and Y axises. When I do
> the following:
> 
> TH2F *ha2 =new TH2F("ha2","ADC",200,-100.,100.,200,-100.,100.);
> TFile f1("tmp_proton.root");
> TNtuple *n1=(TNtuple*)f1.Get("h9");
> n1->Draw("Y:X>>ha2","","scat");
> 
>  The scatter plot is drawn but it does not fit the
> ranges I predifined(-100. to 100.).
> 
> And when I do:
>   ha2->Draw("scat");
> It shows 0 entries and of course draw nothing!
> May be I missed something?
> 
>   Thanks!
>   zhou



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