Grabbing entry number of selection from tree

Is there an easy way to grab the entry numbers from a tree after applying a cut? For example, if I have a tree with branches:

Int_t trignum
Int_t value

and I want to know the tree entry number corresponding to trignum = 20453. I could just loop over entries until I find this value, but my trees are very very large, and this would be too time consuming.

Thanks

Jesse Wodin

see class TEventList or TEntryList

Rene

Hi,

The simplest is to create a TEntryList during the application of the cut:root [1] ntuple->Draw(">>elist","px>3.0","entrylist") (Long64_t)48 root [2] elist->Print("all") ntuple /local2/pcanal/root_working/code/root.untouched/tutorials/hsimple.root 728 857 2485 ....

Cheers,
Philippe.

Does this solution also work for a TChain?

Ah, this seems to work with “eventlist” as opposed to “entrylist.”