[ROOT] merging Ntuples in a single file

From: Eftychios Matathias (felice@grad.physics.sunysb.edu)
Date: Wed Nov 20 2002 - 23:47:47 MET


Dear all,
first of all this is my first message to the roottalk list although I have 
been using root for a couple of years now. My name is Felix Matathias and 
I am a grad student at the Relativistic Heavy Ion Group at the 
State University of New York at Stony Brook and a member of the PHENIX 
collaboration. Enough said :) Root Rocks!


To the problem now:
I have an online monitoring program, always running, that periodically 
writes an ntuple to a file. I open the file, write the ntuple, 
close the file, reset the ntuple, fill new data and the loop continues. 

The problem is that even if I open the file to write in UPDATE mode the 
ntuples are written as diffenent keys/objects instead for a single merged 
ntuple. And therefore a user cannot operate at the prompt and draw the 
entire history.

Is there a way of avoiding this ?

I am familiar with the way to retrieve all the keys and merge them into a 
single Ntuple etc. but I was wondering if root can do such a thing 
automatically. I am considering doing the Autosave()/SaveSelf() trick but 
I am a bit nervous having a file open for such a long period of time. 

Best Regards,
Felix



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