Hi,
This question is simple, but has caused me hours of problems.
I want to read an ntuple and fill a histogram with data from the ntuple
and then write the histgram to another file.
TH1F* h4 = new TH1F("h4","4 MeV Electrons",80,-1,1);
TFile* fout = new TFile("arHistos.root","NEW","AR hists",1);
TFile* ntp = new TFile("cjj_e4.root","READ");
if(ntp->IsOpen())
h509->Draw("(Ue*Uft+Ve*Vft+We*Wft)>>+h4","Rfitt<600",);
Everything to here is fine.
The first problem is that if I
ntp->Close();
h4->Draw();
the histogram is empty. The upper/lower bounds and title are correct
but there is no data in the histogram: I get a flat line at zero counts.
I checked the browser and it turns out that the histogram is "part of"
the file cjj_e4.root (even though I opend it read only.)
I thought I would work around the problem by opening a second file and
writing the histogram to it. That gives an error that the file cjj_e4 is
read-only.
I realize that for just one file, I can keep it open for the duration of
my work, but I will need to take one histogram from each of 6 or 12
files, and it seems inelagant to be forced to keep open that many files.
Also, the histogram is created before any files are opened. When I fill
the histogram with the draw command, why doesn't the data get written to
something with global scope? (ie something that will exist in memory after
the file is closed) I don't understand why that wouldn't be automatically
so.
Thanks for your time and consideration.
Chris.
=================================================================
= =
= Chris Jillings =
= Department of Physics phone/voice mail: (613) 545-6000x4805 =
= Queen's University fax: (613) 545-6813 =
= Kingston, Ontario email: chris@mips2.phy.queensu.ca =
= Canada, K7L 3N6 web: http://snodaq.phy.queensu.ca =
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