Hi Martin,
Yes, of course, you can use the technique I indicated to Bernhard.
This technique reading two or more Trees will work if your Trees
have the same structure.
Rene Brun
Martin Turner wrote:
>
> Hi Rene,
> Thanks for the advice abot using a friend tree but maybe I should have
> mentioned I need to call TTree::MakeSelector().
> I saw in rootalk a solution to the problem if I was using makeclass, which
> I assume would still work, but I also read that I could loop on two trees
> at the same time in the selector file. This sounds what I want,
> or is more efficient to just use your reply to Bernhard below? The two
> trees I am trying to join have the same structure.
>
> Martin.
> Hi Bernhard,
>
> Yes, this is possible. Assuming a TTree *T, on which you have
> generated the class via T->MakeClass("TC");
> I assume that the first tree is in file tree1.root, the second in
> tree2.root
> or subdirectory of tree1.root. You can do
>
> root > .L TC.C
> root > TC t1;
> root > TFile f2("tree2.root");
> root > TTree *tree2 = (TTree*)f2.Get("T");
> root > TC *t2 = new TC(tree2);
>
> The file TC.C can be edited to include the declaration of
> extern TC *t2;
>
> In the loop, you can call t2->GetEntry(ientry);
>
> Rene Brun
>
> On Tue, 7 May 2002, Rene Brun wrote:
>
> > Hi Martin,
> >
> > Martin Turner wrote:
> > >
> > > Hello! does anyone know the answers to the following:
> > >
> > > 1) Open an existing root file containing a tree with a single branch in a
> > > completely different file to the one it was made(easy). Then add
> > > additional variables to this branch which are simple doubles and ints
> > > without overwriting the original branch. If this is possible, are the
> > > additional variables stored at the entry number where it finished last
> > > time or start from scratch.
> > > If (1) is impossible then I may fill the tree with dummy
> > > leaves so that I simply update vertically.
> >
> > The solution is to use Tree Friends.
> > See TTree::AddFriend
> > http://root.cern.ch/root/htmldoc/TTree.html#TTree:AddFriend
> > See example with $ROOTSYS/tutorials/tree3.C
> >
> > > 2) Could someone give an example of how to append entry's to a tree.
> >
> > TFile *f = new TFile("myexistingfile.root","update");
> > TTree *T = (TTree*)f->Get("myTree");
> > T->SetBranchAddress(....
> >
> > your loop with
> > T->Fill();
> >
> > T->Write();
> >
> > Rene Brun
> >
> > >
> > > Thanks in advance
> > > Martin.
> >
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