List of Entries Obeying a Certain Condition from TTree

[LaurenC]

Hi,

I am looking for a way to find a list of Tree entries/indices obeying a condition. The problem is I have multiple variables for each entry and I need to find out which entries pass a selection before using a different variable for a calculation. I have seen the TEntryListArray but I am not sure if this does what I want or how to use it.

Many thanks in advanced!

_ROOT Version: ROOT 6.14/06 Built for linuxx8664gcc

[alexwenym]

How to access the value of branch variables?

Hello, I’m a beginner.I create a file pixels.root and a tree with a pixel branch and totE branch. In my programming, I use a loop ( for (int i=0; i< 36; i++) {pixel =i)};I obtain a histogram corresponding to pixels. My problem: I would like to retrieve the tenth pixel with its energy associated (and so forth) and to create a energy histogram per pixel. Or simply how to access the value of branch variables? TFile *myfile= new TFile(“pixels.root”,“READ”); Ttree tree= (Ttree myfile)->Get(“tre…

See this post. The first answer pretty much does exactly what you want - you can impose your own conditions on certain variables and do other things with other variables in the same event.

[LaurenC]

Hi. I am trying to find a way of not looping over every entry as I have nearly 800,000 entries each with 100ish variables. Is there another way? How does TEntryListArray work?

[pcanal]

Do not use TEntryListArray which is an implementation detail of TEntryLIst (which you should use … maybe) See https://root.cern.ch/doc/master/classTEntryList.html

The simplest maybe to use TTree::Draw:

tree->Draw(">>entrylistname",setofcondition,"entrylist");

See https://root.cern.ch/doc/master/classTTree.html#a73450649dc6e54b5b94516c468523e45