Hi Matt,
I have reported a few times to this list the restrictions in TTree::Draw
regarding multi-dim arrays.
Philippe Canal is currently working on a new algorithm in TTreeFormula
to support 2-d arrays with fix or dynamic size.
Rene Brun
On Wed, 31 May 2000, Matthew D. Langston wrote:
> There seems to be a bug in the "Draw" mechanism of the TTree and TChain
> classes when drawing elements of a multidimensional array.
>
> The problem is that the "Draw" member function of both TTree and TChain
> produce histograms filled with zeroes when one tries to Draw the
> elements of an array.
>
> For example, consider a tree with a branch of type "Float_t E[2][4]".
> The command
>
> root [0] tree->Draw("E[0][0]")
>
> produces a histogram filled with zeroes for all entries. However, after
> I then do this:
>
> root [1] tree->Draw("E")
>
> (i.e. just "histogram the entire array"), then I can index the first
> dimension of the array, but still not the second, i.e. TTree::Draw()
> can discriminate between different indices for the first dimension, but
> seems to ignore the second index of an array. For example, both
> tree->Draw("E[0][0]") and tree->Draw("E[0][1]"), produce the same
> histogram.
>
> The situation is even worse for a TChain, as there doesn't seem to be
> any way to index even the fist dimension of the array.
>
> --
> Matthew D. Langston
> SLD, Stanford Linear Accelerator Center
> langston@SLAC.Stanford.EDU
> 650.926.3279
>
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