(no subject)

Rene Brun (Rene.Brun@cern.ch)
Mon, 23 Jun 1997 16:29:42 +0200

Maarten Bruinsma wrote:
>
> Dear ROOT,
>
> When I want to determine how many entries in my ntuple
> satisfy a certain selection, do I have to give an explicit command that
> the selection-string has to be processed? I have tried the following:
>
> // Calculate efficiencies:
>
> Float_t Ptcut,Pcut;
> Int_t Nr_Selected;
> Int_t Nr_NotSelected;
> Char_t Cuts[80];
> sprintf(Cuts,"sqrt(Px*Px+Py*Py)>0");
> TTreeFormula* Selection = new TTreeFormula("selectionform", Cuts,
> muontuple);
> Nr_NotSelected= muontuple->GetSelectedRows();
>
> for(Ptcut=0;Ptcut<2;Ptcut+=0.1)
> {
> for(Pcut=0;Pcut<20;Pcut+=1)
> {
> sprintf(Cuts," sqrt(Px*Px+Py*Py)> %f && sqrt(Px*Px+Py*Py+Pz*Pz) > %f",
> Ptcut, Pcut);
> Nr_Selected = muontuple->GetSelectedRows();
>
> Efficiencies->Fill(Nr_Selected,Ptcut,Pcut);
>
> }
> }
>
> But somehow the NrSelected is always zero. What should I do?

We do not have a function right now returning the number of events
passing a selection formula. But you can get it with two lines:
Root > muontuple->Draw("Px","your selection", "goff");
Root > muontuple->GetSelectedRows();

Rene Brun