data analysis with ROOT

Got similar results to my previous post with Octave, using ROOT.

Had some hiccups. Initial testing of ROOT C macro failed due to that particular sample data file being empty! The file input was based on this basic.C example. After getting the samples into the ntuple,
while (1) {
      in >> runID >> sID >> energy >> pixelID;
      if (!in.good()) break;
      ntuple->Fill(runID,sID,energy,pixelID);
      nlines++;
   }
I could do a simple linear plot just to check,
ntuple->Draw("pixelID","energy");

Then I created the same sort of 2D matrix as in octave - perhaps this is not necessary, but this is the way I did it :)

 for (int i=0;i<8;i++)
    for (int j=0;j<8;j++)
     {
     energy2D[i][j]=0;    // initializing to zero, since 
                          // some i,j are not mentioned in the next loop
     }

for (int i=0;i<nlines;i++)     {
     ntuple->GetEntry(i);
    //pmtNumber pmtx is an 8x8 array,
    // assumed numbered rowwise.
    //for i=0:7, j=0:7,
    //i*8+j=pmtx. So
    jj= int(pmtx) % 8; //here we need to cast the float pmtx as an int
    ii= (pmtx -jj) / 8;
    energy2D[ii][jj]=enx   
     }

for (int i=0;i<8;i++)
 for (int j=0;j<8;j++)      {
     h2->Fill(i,j,energy2D[i][j]);
     }
h2->Draw("lego2");