[Matplotlib-users] matplotlib:numarray slicing

[Graeme O'K. <gj...@ne...>]

Hi,

I know this really belongs on the sourceforge.net:numarray list, but  
it is a very inactive list.

I have noted the following with numarray:

 >>> x = numarray.zeros([3,3], numarray.Int16)
 >>> i = [0,1,2,0,1,2]
 >>> j = [0,1,2,0,1,2]
 >>> x[i, j] += 1
 >>> print x
[[1, 0, 0]
  [0, 1, 0]
[0, 0, 1]]
I was expecting (hoping)
[[2, 0, 0]
  [0, 2, 0]
  [0, 0, 2]]

which is what you obviously get if you:

for n in range(len(i)) : x[i[n], j[n]] += 1

This is the sort of operation one does all the time when  
histogramming data-streams. Is there a way to achieve this without  
looping over i/j.

cheers,

Graeme