Hi Topher,
You have two possibilities:
-using the return value of Ttree::Draw
int nselected = tree->Draw(selection,selection,"goff");
-using TTreeFormula directly
TTreeFormula select("select","selection,tree);
then in your loop on tree entries,
double r = select.Eval(entry_number);
if (r==0) the selection is not true.
Rene Brun
Topher Cawlfield wrote:
>
> Hi,
>
> Does anyone know how I can (quickly and easily) get a count of events in
> a TTree that pass a certain cut? One method is to make a histogram, use
> TTree::Project to fill it, and then get the total bin contents from
> TH1::GetStats. But this seems unnecessarily tedious and time-consuming,
> creating (and later destroying) a histogram, and requires knowing of a
> dummy variable to bin in.
>
> The reason for this is that I want to make a simple, general-purpose
> utility for creating plots of quantities like yield and S/N for a
> variety of cuts. One common way to assess yield and background is to
> perform a fit. Simpler still, one could perform background subtraction
> (such as sideband, wrong-sign, Monte Carlo, etc.).
>
> So, I thought I'd make a function that takes a baseline cut, an array of
> experimental cuts, and an instance of a subclass of "Evaluator", and
> makes a plot (one point per cut). Evaluator would be an abstract class
> that defines a "getXY" virtual function that takes a cut and returns an
> x, dx, y, and dy. X and Y would be, for example, S/N and yield. Then
> I'd make a derived class, say "EvalSubtract", that you can hand a TTree,
> signal cut, and background cut. The evaluation of signal (or
> background) would simply be a count of events passing both the analysis
> cuts and the signal (or background) cuts. Well, it sounded trivial to
> me, until I ended up searching through the root docs for a TTree member
> function that performed the count. No luck!
>
> I suppose one solution could be to write a counting TSelector and using
> TTree::Process. But I don't know how to write the ProcessCut function
> to evaluate a TCut, or whether or not this is the best way.
>
> Any ideas?
>
> Topher Cawlfield
This archive was generated by hypermail 2b29 : Thu Jan 01 2004 - 17:50:15 MET