[ROOT] TChain Scan/Draw returning different values

From: Caius Howcroft (howcroft@hep.phy.cam.ac.uk)
Date: Tue Nov 05 2002 - 11:30:41 MET


Hi,

root 3.3.09

I have a set of files all with the same trees in (a t_cse and a t_filter).

Here is what happens:

root [0] TChain* ch_ce = new TChain("t_cse")
root [1] ch_ce->Add("./f*.root")
(Int_t)11
root [2] ch_ce->Draw("run:snarl", "projs==1")
<TCanvas::MakeDefCanvas>: created default TCanvas with name c1
(Int_t)20
root [3] ch_ce->Draw("run:snarl", "projs==1")
(Int_t)21
root [4]


you see that I run the same Draw command twice, but the first time it
selects 20 events and the second time it selects 21 events!, This really
worries me if I execute the same bit of code twice I get different
results.  This effect seems to scale with files, and in the total data set
the difference is more than a factor of 2!!!.  This isnt any fancy tree is
just a bog standard tree with bog standard Int_t and Float_t entries.

Exactly the same thing happens for TChain::Scan.


(the files I used to do this are at
http://www.hep.phy.cam.ac.uk/~howcroft/data_trees.tar.gz)

I'm using root 3.03/09 on redhat 7.3, gcc v3.0, i685.

Am I doing somthing really stupid?

Caius


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