Hi HP, The best way to do this is to create a small new Tree containing only the modify branch(es). Then declare this small Tree a friend of your main Tree. see : http://root.cern.ch/root/htmldoc/TTree.html#TTree:AddFriend for more info about Tree friends Rene Brun On Tue, 21 Jan 2003, HP Wei wrote: > hi, > I have not tried out the 'version control' stuff in ROOT. > I figure that it is faster to ask to get answers to the following > questions. > > Suppose I have a big tree (tr) > with several branches and having millions of events. > > Suppose I change the value in event i in one branch (say, br3). > After the tree is saved to the file, > I understand the tree in the file contains the old version > of br3. In addition, the new version of the branch is also saved. > The question is how this is done. > Does the file contain > one WHOLE copy of br3 with event i having the new updated value? > Or does ROOT just store the difference between the new and the old > version ? > > Thanks, > HP >
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