Re: size of a variable

From: Rene Brun <Rene.Brun_at_cern.ch>
Date: Fri, 26 Feb 2010 12:10:16 +0100

Hi Marc,

see the doc of TTree::Draw, in particular this section:

   //
   //     Accessing collection objects
   //     ============================
   //
   //  TTree::Draw default's handling of collections is to assume that any
   //  request on a collection pertain to it content.  For example, if 

fTracks

   //  is a collection of Track objects, the following:
   //      tree->Draw("event.fTracks.fPx");
   //  will plot the value of fPx for each Track objects inside the 

collection.

   //  Also
   //     tree->Draw("event.fTracks.size()");
   //  would plot the result of the member function Track::size() for each
   //  Track object inside the collection.
   //  To access information about the collection itself, TTree::Draw 

support

   // the '@' notation. If a variable which points to a collection is prefixed

   // or postfixed with '@', the next part of the expression will pertain to

   //  the collection object.  For example:
   //     tree->Draw("event._at_fTracks.size()");
   //  will plot the size of the collection refered to by fTracks (i.e 

the number

   // of Track objects).

Rene

Marc Escalier wrote:
> Hello,
>
> would somebody know how to the following functionnality :
> let's assume a TTree has a variable myvar with myvar[0], myvar[1],
> ..., myvar[N]
> with N varying from event to events
>
> Is there a way to draw the histogram of the size of the myvar
> *without* doing the stuff of SetBranchAddress, etc... to get the
> variable then doing myvar->size()
> and so on
>
> ==>I mean, is that possible to do that in a very short way like :
> mytree->Draw("myvariable.TheMethodToGetTheSize()")
> or
> mytree->Project("myhisto","myvariable.TheMethodToGetTheSize()")
>
> thank you
>
Received on Fri Feb 26 2010 - 12:10:47 CET