[Numpy-discussion] efficient sum of "sparse" 2D arrays?
Kuzminski, Stefan R
SKuzminski at fairisaac.com
Mon Jan 26 04:54:03 CST 2004
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: numpy-discussion-admin at lists.sourceforge.net
[mailto:numpy-discussion-admin at lists.sourceforge.net] On Behalf Of
Konrad Hinsen
Sent: Monday, January 26, 2004 12:17 AM
To: RJS
Cc: numpy-discussion at lists.sourceforge.net
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
> 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.
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