[Numpy-discussion] indexing question

Todd Miller jmiller at stsci.edu
Sat Mar 27 13:57:51 CST 2004


On Sat, 2004-03-27 at 12:05, Faheem Mitha wrote:
> Dear People,
> 
> Suppose I create a numarray arry (say). A numeric array would be fine
> too; it probably does not matter.
> 
> >>>import numarray
> >>>foo = numarray.reshape(numarray.arange(9),(3,3))
> array([[ 0,  1,  2,  3],
>        [ 4,  5,  6,  7],
>        [ 8,  9, 10, 11],
>        [12, 13, 14, 15]])
> 
> Is there some way to select the indexes corresponding only to (say)
> two rows or columns?
> 
> ie suppose I just want the first and the fourth row or the first and
> third columns? Is there some clean way to do this which does not
> involve extracting individual rows or columns?
> 
> Ie. I want something like
> >>> foo[?,:]
> array([[ 0,  1,  2,  3],
>        [12, 13, 14, 15]])
> 

Try foo[[0,2]].  Note that the array indexing syntax is a little picky: 
foo[(0,2)] (tuple index) won't work,  just foo[[0,2]] (list index) or
foo[array([0,2])] (array index).

Regards,
Todd

> etc.
> 
> Suggestions appreciated. Please cc me; I'm not subscribed. Thanks in
> advance.
> 
>                                                Faheem.
> 
> 
> 
> 
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-- 
Todd Miller <jmiller at stsci.edu>





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