[SciPy-user] extracting elements of a matrix using arrays as indices

Alan G Isaac aisaac@american....
Wed May 21 14:29:35 CDT 2008


On Tue, May 20, 2008 at 9:43 PM, Michael Hearne <mhearne@usgs.gov> wrote:
> Neilen - Thanks.  Unfortunately, I've either discovered 
> a bug or have failed to understand how to use this 
> function.  The below code snippet:
> from pylab import * 
> import numpy 
> print numpy.__version__, numpy.__file__ 
> data = rand(648,690)
> i,j = (data < 0.14).nonzero()
> data[ix_(i,j)] = data[ix_(i,j)]*0 

I believe your problem is with ``data[ix_(i,j)]``.
Let's say that i and j are about 60,000 in length.
So you are trying to create a 60k × 60k array,
which has 3600M elements. I'm guessing you do not
have enough memory for this. Otherwise, it should
work (although it is very wasteful).

hth,
Alan Isaac





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