TTree Draw loop over matrix elements twice

ROOT
1

tree->Draw(“matrix[ ] : matrix[ ] >> hist2D”) draws a 45 degree line
What I would like is the draw to loop over the matrix elements twice: one for each occurrence of matrix[ ]
My desired output is a 2D histogram with points at
matrix[0] : matrix[0]
matrix[1] : matrix[0]
matrix[2] : matrix[0]
…
matrix[0] : matrix[1]
matrix[1] : matrix[1]
matrix[2] : matrix[1]
…
…
I haven’t found a clear way to do this yet, can someone point me to the post that solves this?
-Leo

2

Hi Leo,

unfortunately the TTree::Draw syntax does not yet support nested loops.

Cheers,
Danilo

3

You could call several times Draw on the same histogram using the + option.

TH2* h2 = new TH2F("hist2D","title", <set your binning>);

tree->Draw("matrix[ ] : matrix[0] >> hist2D");
tree->Draw("matrix[ ] : matrix[1] >>+ hist2D");
tree->Draw("matrix[ ] : matrix[2] >>+ hist2D");

See root.cern.ch/doc/master/classTT … 3c70bfe8d7