Hi Vitaliy, Yes, this should be straightforward. Follow the following steps; 1- connect the original file "first.root" with TTree T1 2- Set branch addresses for T1 3- Create new file "second.root" 4- Create new TTree T2 5- Create branches pointing to the old variables 6- Create new variables 7- Execute event loop - for each entry T1->GetEntry(i); - modify old variables in memory, compute new variable - T2->Fill() You can simplify steps 4 and 5 by using TTree::cloneTree or TTree::CopyTree. See examples of use in $ROOTSYS/test/stress.cxx See also examples in $ROOTSYS/tutorials/copytree.C and copytree2.C Rene Brun Vitaliy Ziskin wrote: > > Hello, > Is there a way to take an ntuple and apply specific cuts on some entries > and modify/calibrate other and print a set of midified collumns into a new > ntuple. It sounds easy but (at least the way I see it) the ntuples are > written row-wise and read collumn-wise. > > Thanks, Vitaliy > > ===================================================================== > Vitaliy Ziskin Tel: (617)253-7065 > MIT 26-547 http://www.lns.mit.edu/people/vziskin/ > 77 Massachusetts Ave > Cambridge, Ma > 02139 > ====================================================================== > "The memories of a man in his old age > Are the deeds of a man in his prime"--Pink Floyd
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