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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