Question about TH1F

Newbie
1 
root [8] TH1F *hist=new TH1F("tt","tt",1000,-1,1);
root [9] tree->Draw("nbdt>>hist","track.rgt2[0]/rich.beta*::TMath::Sqrt(1-rich.beta*rich.beta)<-1.5&&track.rgt2[0]/rich.beta*::TMath::Sqrt(1-rich.beta*rich.beta)>-2&&nbdt>-8")
Info in <TCanvas::MakeDefCanvas>:  created default TCanvas with name c1
(long long) 36313
root [10] hist->Draw()
Info in <TCanvas::MakeDefCanvas>:  created default TCanvas with name c1

I redirect the drawing to hist, however, hist is empty, why?

2

Hello,

Can you try to repeat the operation with no selection, and then incrementally add cuts?
Moreover, please consider using RDataFrame for this kind of operations: it is intuitive, performant and well supported and your productivity might increase!

Cheers,
D

3

Hi,
I repeat it with no selection:
root [7] TH1F *hist=new TH1F()
(TH1F *) 0x4b14c40
root [8] Int_t a=tree->Draw(“nbdt>>hist”,“”,“goff”)
(int) 6940509
root [9] hist->GetEntries()
(double) 0.0000000
root [10]
There is still something wrong.

4

Try with:

   TH1F *hist=new TH1F("tt","tt",1000,-1,1);
   tree->Draw("nbdt>>tt","","goff")

Or:

   TH1F *hist=new TH1F("hist","tt",1000,-1,1);
   tree->Draw("nbdt>>hist","","goff")
5

Thank you, it works. It seems that the redirect method looking forward to the name of hist instead of the pointer :smiley:

1 Like
6

Thanks @bellenot ! I did not see that, my bad. Indeed it cannot see the name of the C++ variable, however, the name of the ROOT object yes, it’s registered.

Glad to see you can move forward!

2 Likes