Friend trees of "filtered Trees"

From: Tim Head <betatim_at_gmail.com>
Date: Sun, 21 Jun 2009 12:16:52 -0500

Apologies, in a first attempt I messed up the reply-to-all.

Hello,

2009/6/19 Salvatore Rappoccio <rappocc_at_fnal.gov>:
> Hi, All,
>
> I was wondering how easy it is for a TTree to access a "friend" TTree when
> the events of the first tree are a subset of the second? The application
> would be where the user filters events from one TTree and drops some
> branches, but then wants to access the original for debugging purposes.
>
> I've only used friend trees when there is an event-by-event match. Is this
> functionality possible directly with friend TTrees?

I am not sure if there is a builtin way of doing this in ROOT, a while ago I needed something similar and came up with the following:

def befriendtrees(pruned, unpruned, cut="1"):    """Apply cut to the unpruned tree so that it has the same entries as the pruned

   tree.
   """
   # Make a copy of unprunedtree which has events removed
   copy = unpruned.CopyTree(cut)

   if copy.GetEntries() != pruned.GetEntries():

       msg = "Number of events differ after applying the cut"        raise RuntimeError(msg)

   # XXX maybe some work needs to be done with SetDirectory() for the copied tree

   pruned.AddFriend(copy)
   return pruned

It works quite well for me, not sure how well it does with _huge_ trees and whether or not you need to SetDirectory() for the copied tree or not. Trees that are not attached to a file seem to have some issues sometimes

HTH,
Tim

>
> Thanks,
> Sal Rappoccio
>

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Received on Sun Jun 21 2009 - 19:17:02 CEST