I mean that TTree entries are sorted using the BuildIndex() function. Then a new TTree is filled with the sorted entries. All of this is done in RAM. For details, see an old post of mine:
[url]Create a new index for a TTree - #8 by Adrian
I adopted the strategy given by Wile E. Coyote.
If you have a better approach, I’d be happy to hear it.
Cheers.