Hi Dmitriy,
TTree::CloneTree returns a clone of the original object. In case of a TChain,
CloneTree returns a TChain*. You cannot fill a TChain, only a TTree.
I suggest the following changes in your code:
void filter()
{
TChain *chain = new TChain("Global");
chain->Add("file1.root");
chain->Add("file2.root");
chain->Add("file3.root");
cout << " Creating new root-file ..."<< endl;
TFile *newFile = new TFile("small.root","recreate");
cout << " Creating new tree ..."<< endl;
TChain *newchain = (TChain*)chain->CloneTree(0); //<====
TTree *tree = newchain->GetTree(); //<=====
if (fChain == 0) return;
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,
nb = fChain->GetEntry(jentry); nbytes += nb;
if ( SelectionFunction() ) tree->Fill();
}// end loop over events
newFile->cd();
tree->Write();
}
Rene Brun
Dmitriy Bandourine wrote:
>
> Hi rooters,
>
> I need to filter out the events containing in the chain
> of root-files using some function INSIDE the loop over events
> and then save them in new tree with analogous branch structure.
> The method with
> TTree *tree = chain.CloneTree(Tcut);
> does not suit me because, as mentioned above, I need to use a
> selection function, which return value depends on the event parameters.
>
> My script looks like this:
> #===========================================
> void filter()
> {
> TChain *chain = new TChain("Global");
> chain->Add("file1.root");
> chain->Add("file2.root");
> chain->Add("file3.root");
>
> cout << " Creating new root-file ..."<< endl;
> TFile *newFile = new TFile("small.root","recreate");
> cout << " Creating new tree ..."<< endl;
> TTree *tree = chain.CloneTree(0);
>
> if (fChain == 0) return;
> 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,
> nb = fChain->GetEntry(jentry); nbytes += nb;
>
> if ( SelectionFunction() ) tree->Fill();
>
> }// end loop over events
>
> newFile->cd();
> tree->Write();
> }
> #==============================================
>
> For 3.01.06 in this case I get:
> Warning in <TChain::Fill()>: may not use this method
> and nothing written to "tree".
> For 3.02.07 I get:
> *** Break *** segmentation violation
>
> How to initialize properly "tree"?
> Obviously, the string:
> TTree *tree = chain.CloneTree(0);
> does not help
>
> Thanks in advance,
> Dmitri
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