Re: Keeping Histograms

From: Pasha Murat (murat@cdfsga.fnal.gov)
Date: Wed Nov 04 1998 - 04:43:35 MET


Jeff Patterson writes:
 > Hey Rooters,
 > 
 >         My problem is that my histrograms keep disappearing from memory.
 > Here is what I am doing.  I have an row-wise Ntuple from HBook that I have
 > converted with h2root.  The ntuple is called h666.  So I open the file,
 > make the histogram, then I want to clode the Ntuple and open another one
 > and add to it.  But as soon as I close the file, I lose the histogram.
 > How can I get around this.  Sample code
 > 
 >         f1 = new TFile("ntup1");
 >         MOM = new TH1F(bins);
 >         h666->Draw("mom>>+MOM", "cuts");
 >         delete f1       //This is were I lose my histogram
 >         f1 = new TFile("ntup2");
 >         MOM = new TH1F(bins);
 >         h666->Draw("mom>>+MOM", "cuts");
 >           etc.....
 > 
 > What am I doing wrong.
 > 
 > 					Jeff Patterson
 > 


Jeff: when you create a histogram after haaving opened a file, ROOT associates 
it with this file, so when you delete the file, your histogram also gets deleted.
If you don't want to save `h666' into a file, simple inversion

         MOM = new TH1F(bins);
         f1 = new TFile("ntup1");

will do the job and your histogram will remain in memory after you close `f1'. 

							- regards, pasha.



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