Hi Jiri,
> and T->Draw("GetEntries()") (fTracks.GetEntries()).
Note that in TTree::Draw you can never directly call the methods of
a TClonesArray. TClonesArray are treated as a special case to make them
appear (for convenience) as simple arrays of their content.
Thus when you use 'T->Draw("GetEntries()")' it is NOT equivalent to
'T->Draw("fTracks.GetEntries()")' [this last syntax would try to call
Track::GetEntries]
Also, TTree::Draw implemenents one more convenience in that it allows
the user to omit the left most part of qualifier. Thus when you
use 'T->Draw("GetEntries()")', TTree::Draw look for the Method
GetEntries, first in the main object (Event) and then in each of the
leaf of the TTree (more or so each of the data members). Thus it
calls fEntries on the first 'leaf' where it can. In the Event case,
calling 'T->Draw("GetEntries()");' is actually equivalent to
T->Draw("fHighPt.GetEntries()");'.
Cheers,
Philippe.
-----Original Message-----
From: owner-roottalk@pcroot.cern.ch
[mailto:owner-roottalk@pcroot.cern.ch]On Behalf Of Jiri Masik
Sent: Wednesday, February 13, 2002 6:10 AM
To: roottalk@pcroot.cern.ch
Subject: [ROOT] test/Event example
Hi,
I examined the Event demo in the test directory and found something
which I do not understand. I run ./Event to produce Event.root, then
T->Draw() to obtain tree variables. The results on the number of
tracks are different for T->Draw("fNtrack") and
T->Draw("GetEntries()") (fTracks.GetEntries()). The first one is
populated around 600 while the second one is typically 360.
When events are written on file both numbers are equal.
What's wrong? Is it a bug?
cheers
Jiri
linuxdeb2ppc, gcc-3.0, Root-3.03 from 10/02
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