Hello,
Is it possible to tell the Draw() function to draw only the first iteration having passed the selection criteria ?
For exemple something like this :
tree->Draw(“array”,“array>1 && onlyfirst”)
would fill only the first element of array that is greater than 1 in each event.
cheers,
P-A
Hi,
There is no easy way (that I know of) of doing this with a formula.
You need to either either MakeSelector or MakeProxy or to pass a script to Draw. Something like:void onlyfirst() {
Int_t len = ... here grab the length of your array ...;
for(int i=0;i < len; ++i) {
if (array[i]>1) {
htemp->Fill(array[i);
return;
}
}
and usetree->Draw("onlyfirst.C","","nohist");
Cheers,
Philippe
Hello,
For those interrested I found an other solution.
I use the code generated by MakeClass() from my tree and then define a Draw() like method :
void WZan::DrawFirst(TString varexp, TString selection, Option_t* option , Long64_t nentries , Long64_t firstentry )
{
if (fChain == 0) return;
nentries = (nentries < fChain->GetEntriesFast() ) ? : nentries , fChain->GetEntriesFast() ;
fChain->Draw(varexp,selection,"",1);
TTreeFormula *exp = fChain->GetVar1();
TTreeFormula *sel = fChain->GetSelect();
m_histo->Reset();
cout << exp << endl;
Int_t nbytes = 0, nb = 0;
for (Long64_t jentry=firstentry; jentry<nentries;jentry++) {
Long64_t ientry = LoadTree(jentry);
if (ientry < 0) break;
nb = fChain->GetEntry(jentry); nbytes += nb;
bool doplot=false;
int i=0;
if(sel) {for(i=0;i<exp->GetNdata();i++){
if(sel->EvalInstance(i) > 0){doplot=true; break;}
}
} else doplot = true;
if(doplot) m_histo->Fill(exp->EvalInstance(i));
}
m_histo->Draw(option);
}Here you need to add a TH1* member to the class and have it valid before the call of the function.
Load it compiled, so the execution is not too long (using .“L theclass.C++”).
I find it to work well.
The remaining problems : only 1D graph, and no automatique computing of the histo range as in TTree::Draw(), and “same” option won’t work.
PA