XML data from TH3F

[biblue]

Hi, I’m a beginner in ROOT and I’m having trouble to interpret a .xml data from a TH3F ROOT file.
Here is the macro

void dump(const char *fname = "resultwaterboneEdep.root",
          const char *nname = "histo")
{
  if (!fname || !(*fname) || !nname || !(*nname)) return; // just a precaution
  TFile *f = TFile::Open(fname, "READ");
  if (!f) return; // just a precaution
  TH3F *t; f->GetObject(nname, t);
  if (!t) { delete f; return; } // just a precaution
  // See:
  // http://root.cern.ch/root/html/TTreePlayer.html#TTreePlayer:Scan
  // http://root.cern.ch/root/html/TTree.html#TTree:Scan
  TAxis *xaxis = t->GetXaxis();

  // See:
  // http://root.cern.ch/root/html/TObject.html#TObject:SaveAs
  t->SaveAs("dumpX.xml");
  // t->SaveAs(TString::Format("%s.xml", nname));
  delete f; // no longer needed (automatically deletes "t")
}

This code gives me a .xml file

(...)
<TArrayF>
          <Int_t v="778688"/>
          <Array>
            <Float_t v="0.000000e+00" cnt="194811"/>
            <Float_t v="2.422105e-03"/>
            <Float_t v="0.000000e+00" cnt="261"/>
            <Float_t v="4.438538e-03"/>
            <Float_t v="0.000000e+00" cnt="5"/>
            <Float_t v="3.366382e-02"/>
(...)

What is v? and cnt? and why there is a zero and a number in sequence (for the most part)?

[linev]

Hi,

Here attribute v contains values of array elements.
And then cnt attribute present, means there are as many similar consecutive elements. Minimal possible value is 2.

Regards,
Sergey

[biblue]

Hi linev,

Thank you so much! But do you think these Float_t are only ‘v’ values for X coordinate?

[linev]

Hi,

In the array bins content is stored.
For 3-dimensional histogram with NxMxK bins total number of
elements in such array is (N+2)*(M+2)*(K+2),
while it also includes overflow/underflow bins.

Probably, you should start with 1-dim histogram to understand better
which values corresponds to which histogram bins. In 1 dimensional histogram
it is only two additional values - underflow bin in the beginning and overflow bin at the end.

More info about direct access of bins content you will find here:

https://root.cern/doc/master/classTH1.html

search a paragraph “Convention for numbering bins”

Regards,
Sergey