Instead using Draw to plot histograms of the individual entries
in the root ntuple I would like to create histograms and fill them
with selected entries in the ntuple. I am not quite sure how to do it
after reading the existing documentation. In the next version of
the included macro I would create 2 x 27 x 27 histograms of the
same quantities and save them into a file.
Thanks in advance for help.
Michal Lijowski
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Michal Lijowski Washington University
Research Associate St. Louis, MO 63130-4899, USA
Department of Physics phone: 314-935-6285
Campus Box 1105 email: lijowski@cosray2.wustl.edu
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// read HBOOK generated ntuple and produce histograms of dx2 and dy2
void make_dxdy_hists()
{
gROOT->Reset();
// Connect CRIS ROOT ntuple file generated by h2root
// from the HBOOK make_cris_ntuple.rz file
TFile *f1 = new TFile("/data3/users/lijowski/make_cris_ntuple.root.1");
f1 -> ls();
// connect a tree to an ntuple in the input file
TTree *t9000 = (TTree*)f1 -> Get("h9000;1");
t9000 -> Print();
// create a new Root file
TFile *top = new TFile("dxdy_hists.root", "recreate");
// create a new subdirectory in this file
TDirectory *cdTOP = top -> mkdir("TOP");
cdTOP -> cd();
// create two histograms one for dx2 and another for dy2
char hname[20];
char htitle[80];
Float_t xmin = -1.2, xmax = 1.2;
Int_t nbins = 120;
sprintf(hname, "H2X-plane-dx2");
sprintf(htitle,"H2 X plane dx2");
TH1F *h2x = new TH1F(hname, htitle, nbins, xmin, xmax);
// h2x -> Fill(dx2);
sprintf(hname, "H2Y-plane-dy2");
sprintf(htitle,"H2 Y plane dy2");
TH1F *h2y = new TH1F(hname, htitle, nbins, xmin, xmax);
// h2y -> Fill(dy2);
// save histogram hierarchy in the file
top -> Write();
}