Hi Dmitryi,
Could you try the following variant?
TChain *chain = new TChain("Global");
chain->Add("file1.root");
chain->Add("file2.root");
chain->Add("file3.root");
chain->GetEntry(0); //<========new line
TFile *newFile = new TFile("small.root","recreate");
TTree *tree = (TTree*)chain->GetTree()->CloneTree(0); //<===new line
Rene Brun
//<=====Dmitriy Bandourine wrote:
>
> Thank you Rene!
>
> With your changes ew tree was created and written to the file "small.root"
> But when I tried to read this tree in new session, I got:
> *----
> Error in <TFile::ReadBuffer>: error reading all requested bytes from file small.root, got 0 of 26444
> *---
>
> When I clicked on some leaf in one of braches of the tree in "small.root", I got
> *---
> root [2] <TCanvas::MakeDefCanvas>: created default TCanvas with name c1
> Error in <TFile::ReadBuffer>: error reading all requested bytes from file small.root, got 0 of 26444
> C++ runtime abort: terminate() called by the exception handling mechanism.
> *---
>
> I expect that the size of the created "small.root" file should be at
> least 5-6 times larger than it is.
>
> - Dmitriy -
>
> On Fri, 1 Feb 2002, Rene Brun wrote:
>
> > 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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