The logic in your second small program is wrong.
You should do something like:
{
static Float_t ptot,event;
TFile *f = new TFile("/scratch3/munir/mini/run09666tree2.root");
TTree *trktree = (TTree *) f->Get("trktree");
trktree->SetBranchAddress("event", &event);
trktree->SetBranchAddress("ptot", &ptot);
TH1F *pid1 = new TH1F("pid1","ptot", 100,0,10);
TH1F *pid2 = new TH1F("pid2","events", 200,3000,5000);
Int_t nrow = trktree->GetEntries();
for (Int_t i =0; i < nrow; i++) {
trktree->GetEntry(i);
pid1->Fill(ptot);
pid2->Fill(event);
}
}
Rene Brun
On Tue, 31 Oct 2000, Munir Uzzaman wrote:
>
> Hi Rooters!
>
> I was trying to read (and draw from) a tree which has members named
> "event", "ptot" and many more. when i try to read them in the following
> way:
>
> -------------------------------------------------------------------
> {
> TChain t("trktree");
> t->Add("/scratch3/munir/mini/run09666tree2.root");
> TH1F *pid1 = new TH1F("pid1","ptot", 100,0,10);
> TH1F *pid2 = new TH1F("pid2","events", 200,3000,5000);
> t->Draw("ptot >> pid1");
> t->Draw("event >> pid2");
> }
> ___________________________________________________________________
> things work fine.
>
> BUT, when i do the following
> ------------------------------------------------------------------
> {
> Float_t ptot,event;
> TFile *f = new TFile("/scratch3/munir/mini/run09666tree2.root");
> TTree *trktree = (TTree *) f->Get("trktree");
> TH1F *pid1 = new TH1F("pid1","ptot", 100,0,10);
> TH1F *pid2 = new TH1F("pid2","events", 200,3000,5000);
>
> Int_t nrow = trktree->GetEntries();
> for (Int_t i =0; i < nrow; i++)
> {
> trktree->GetEntry(i);
> trktree->SetBranchAddress("event", &event);
> trktree->SetBranchAddress("ptot", &ptot);
> pid1->Fill(ptot);
> pid2->Fill(event);
> }
> }
> ----------------------------------------------------------------------
> ptot is ok, BUT ALL ENTRIES FOR "event" ARE 0!!!
>
> I really have no clue why is this happening. I'd really appreciate if
> anyone could point me where i am commiting mistake.
>
> Regards,
>
> -munir
> -----------------------------------------------------------------------------
> M. MUNIRuzzaman
> ------------------------------------------------------------------------------
> Graduate Student |email: |Phone:
> Department of Physics |munir@bnl.gov |(909)-787-7401
> University of California | |(909)-276-4703(Home)
> Riverside, CA 92521 |web: |
> USA |www.phenix.bnl.gov/~munir |
> ------------------------------------------------------------------------------
>
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