RE: [ROOT] TNtuple::Draw("sth>>hist") and hist->Write() didn't work

From: Philippe Canal (pcanal@fnal.gov)
Date: Tue Jul 22 2003 - 04:06:51 MEST 

Hi,

Do:
        TFile f(input);
        TCut runcut=cut1 && cut2 && cut3;
        TTree *all = (TTree*)f.Get("all");

        TFile fout(output,"RECREATE");
        TH1F *pointetah = new TH1F("pointetah","emc point eta",80,-1,1);

        all->Draw("pointeta>>pointetah",runcut);

        fout.Write();

The problem is that

        all->Draw("pointeta>>pointetah",runcut);

looks for an histogram named 'pointetah' in the current ROOT directory
and if it does not find one, create one with that name.

In your script, you create histrograms which are stored in the current
directory
at the time (gROOT) and then open the input file, which becomes the current
directory.  all->Draw does not find the histograms in this new current
directory
and thus creates some new ones (and display them properly).  Later when you
call
Write on the histogram pointers, the first histograms (that were held in
gROOT
and are still empty) are saved in the file.

Cheers,
Philippe.


-----Original Message-----
From: owner-roottalk@pcroot.cern.ch
[mailto:owner-roottalk@pcroot.cern.ch]On Behalf Of Weijiang Dong
Sent: Monday, July 21, 2003 7:59 PM
To: roottalk@pcroot.cern.ch
Subject: [ROOT] TNtuple::Draw("sth>>hist") and hist->Write() didn't work


Hi,
I have a root file which contains a Ntuple. I want to draw some of the
variables in the Ntuple into a few histograms and save the histograms into
a new root file. I have a macro to do this. When the macro ran, root
didn't complain anything. But later when I open the new root file, the
histogram keys were visible, but they were all empty. Need your help!
btw, when I do it step by step, I can see the histrograms were correctly
plotted on the canvas, but none of them were correctly wrote into the new
root file.

here is my macro(xbadrun.C):

xbadrun(const char* input, const char* output)
{

        TH1F *pointetah = new TH1F("pointetah","emc point eta",80,-1,1);
        TH1F *pointphih = new TH1F("pointphih","emc point
phi",240,-TMath::Pi(),TMath::Pi());

        TH2F *pointetaphih = new TH2F("pointetaphih","emc point eta and
phi",80,-1,1,240,-TMath::Pi(),TMath::Pi());
        TFile f(input);
        TCut cut1="RunId!=4033025";
        TCut cut2="RunId!=4034002";
        TCut cut3="RunId!=4034005";
        TCut runcut=cut1 && cut2 && cut3;

        all->Draw("pointeta>>pointetah",runcut);
        all->Draw("pointphi>>pointphih",runcut);
        all->Draw("pointeta:pointphi>>pointetaphih",runcut);

        TFile fout(output,"RECREATE");
        fout.cd();
        pointetah->Write();
        pointphih->Write();
        pointetaphih->Write();

        fout.Close();
        f.Close();
}

Thanks.
Weijiang

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