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

[Kuzminski, S. R <SKu...@fa...>]

Could you use masked arrays more efficiently in this case? If you create
the array so that values >255 and <0 are masked, then they will be
excluded from the sum ( and from any other operations as well ).

Stefan


-----Original Message-----
From: num...@li...
[mailto:num...@li...] On Behalf Of
Konrad Hinsen
Sent: Monday, January 26, 2004 12:17 AM
To: RJS
Cc: num...@li...
Subject: Re: [Numpy-discussion] efficient sum of "sparse" 2D arrays?

On 26.01.2004, at 07:14, RJS wrote:

> The problem: I have a "stack" of 8,  640 x 480 integer image arrays=20
> from a FITS cube concatenated into a 3D array, and I want to sum each=20
> 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.



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