[Numpy-discussion] efficient sum of "sparse" 2D arrays?

[Konrad Hinsen]

On 26.01.2004, at 07:14, RJS wrote:

> The problem: I have a "stack" of 8,  640 x 480 integer image arrays 
> from a FITS cube concatenated into a 3D array, and I want to sum each 
> pixel such that the result ignores clipped values (255+); i.e., if two 
> images have clipped pixels at (x,y) the result along z will be the sum 
> of the other 6.
>
Memory doesn't seem critical for such small arrays, so you can just do

sum([where(a < 255, a, 0) for a in images])

Konrad.