[ROOT] using LoadTree with a TChain

From: Ken Bloom (kenbloom@umich.edu)
Date: Sun Jan 06 2002 - 00:31:29 MET


Dear ROOT,

	I have what seems to me like a simple problem...yet I cannot find any 
information about it on the ROOT Web site.  My apologies if I'm asking about 
an already-solved problem.

	I created a TChain that has seven different files as part of it, and I 
used the MakeClass method to write a code skeleton for analysis.  The Loop 
method includes the lines

   Int_t nentries = Int_t(fChain->GetEntries());

   Int_t nbytes = 0, nb = 0;
   for (Int_t jentry=0; jentry<nentries;jentry++) {
      Int_t ientry = LoadTree(jentry); //in case of a TChain, ientry is the entry number in the current file
      nb = fChain->GetEntry(jentry);   nbytes += nb;

The comment line next to LoadTree seems quite true.  fChain->GetEntries() does 
seem to return the number of entries in the entire chain (all seven files), 
yet LoadTree doesn't know what to do once jentry gets to be larger than the 
number of entries in the first file in the chain.  How can I get LoadTree to 
point me to right entry number?  How do we know what the "current file" is, 
and how can we know the number of entries in that particular file?  Thanks for 
your help, best wishes.

						Ken

------------------------------------------------------------------------------
Ken Bloom, Karma Adjuster                                Department of Physics
734-763-2329 / 734-936-1817 (fax)                       University of Michigan
kenbloom@umich.edu                              http://www.umich.edu/~kenbloom



This archive was generated by hypermail 2b29 : Sat Jan 04 2003 - 23:50:37 MET