Hi Gene,
I agree with your comments. Note that is is not complicated to obtain
what you want with the current version and with no changes to ROOT.
Simply, make your TTreeFormula known to the list of formula, eg:
TTreeFormula f3("form3","v1+4",t1);
gROOT->GetListOfFunctions()->Add(&f3); //<====add this line
TTreeFormula f4("form4","form3+v1",t1);
Rene Brun
Gene Van Buren wrote:
>
> Hi. I'm curious as to why TTreeFormula does not recognize
> other TTreeFormulas during Analyze()? It does recognize
> normal TFormulas, but not TTreeFormulas.
>
> For example, let's say I have a TTree* t1 with variable v1:
>
> This works:
>
> TFormula f1("form1","3+5");
> TTreeFormula f2("form2","form1+v1",t1);
>
> But this does not:
>
> TTreeFormula f3("form3","v1+4",t1);
> TTreeFormula f4("form4","form3+v1",t1);
>
> When creating f4, it cannot find form3. It seems useful to me
> that a TTreeFormula associated with a given TTree
> be able to use any other TTreeFormula associated
> with that TTree. This would simply mean that each TTree
> keeps a list of its associated formulae, just as gROOT keeps
> a list of regular TFormulas, and that this list be searched
> for matching formula names within Analyze().
>
> On the technical side, I think this could be done by moving
> the "Look for an already defined expression" portion of
> Analyze() into a second member function
> AnalyzeDefinedExpression() or something like that, which
> would be virtual and re-defined in TTreeFormula so that
> it can search the associated TTree's list of formula in
> addition to gROOT's list.
>
> Another way to do it would be to add a line in TFormula at:
> oldformula =
> (TFormula*)gROOT->GetListOfFunctions()->FindObject((const char*)chaine);
>
> if (!oldformula) oldformula =
> LookForSpecialFormula(chaine);
>
> Then, TFormula* LookForSpecialFormula() could be a virtual
> function with {return 0;} in TFormula, but a search of the
> associated TTree's formulas in TTreeFormula.
>
> The end result of all of this would be that someone could define
> TTreeFormula's to use in the TTree::Scan() and TTree::Draw()
> member functions. That would be nice:
>
> (t1 points to a TTree with variables Px,Py,rapidity)
> TTreeFormula f5("Pt","sqrt((Px^2)+(Py^2))",t1);
> t1->Draw("Pt:rapidity");
>
> -Gene Van Buren
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