Tree::Draw and multiple loops with two arrays

ROOT
1

Hi

I have a branch with an object Spectrometer, which has two object of type Detector. The Detector has 2 arrays *fX and fY with fNhits elements. I need to plot a TH2F histogram where for each X[i] all the Y[j] (j=0;j<fNhit) are plotted. I have looked at the TTree::Draw documentation and the forum but could not find anything that seems quick and easy to use. The closest solution I found seems to be using MakeProxy, but we don’t want (if possible) to have separate files with scripts spread around.

Thanks.

Luiz

2

This is documented with several examples in the Users Guide.
do, eg
T.Draw(“det1.fY:det1.fX”)

Rene

3

Thas is not exactly what I want. This will plot the pairs:
y[0]:x[0]
y[1]:x[1]
y[2]:x[2]
y[3]:x[3]
…

but what I need is:

y[0]:x[0]
y[0]:x[1]
y[0]:x[2]
…
y[1]:x[0]
y[1]:x[1]
…

Unless I completely misunderstood the manual.

Thanks

Luiz

4

Hi Luiz,

Indeed TTree::Draw does not have syntax (expect if using a separate scrip) to implement what you need directly.

The closest should be the following (inefficient) trick:

for (int i=0;i<max_x_size,++i) { tree->Draw(Form("X[%d]:Y>>+myhist",i)); }

Cheers,
Philippe.