Re: How to fill 2D from Ntuple?

Rene Brun (Rene.Brun@cern.ch)
Wed, 03 Feb 1999 08:50:27 +0100

William Love wrote:
>
> Root experts (Valery gave up)
>
> I am trying to dump two 2D arrays from an ntuple to two TH2F's so I
> can subtract them. The arrays are 56X29 so I predefine the output arrays
>
> TH2F hv6("hv6","fooey",56,-0.5,55.5,29,-0.5,28.5)
>
> I then try to fill the array with
>
> ntb->Draw("index:irad>>hv6","bzme*(index<29 && iphi==9)","lego")
>
> If I inspect hv6 beforehand it is 56X29 as expected. After the fill
> the array is 40X40 with the consequent mismatch of the binning and
> the data. What am I doing wrong? I have the results of hv6.Dump()
> both before and after the Draw if you want to look at them.
>
> Bill Love

Hi Bill,
A workaround is to draw the TH2F with the option "lego" before
calling TTree::Draw and then use the option "same" in Draw.
TH2F hv6("hv6",....);
hv6.Draw("lego");
ntb->Draw("index:irad>>hv6","...","legosame")

I will adapt the algorithm to be automatic.

Rene Brun