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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