[Numpy-discussion] On responding to dubious ideas (was: Re: Advanced indexing: "fancy" vs. orthogonal)

[Jaime Fernández del Río]

On Thu, Apr 9, 2015 at 8:26 PM, Alexander Belopolsky <ndarray at mac.com>
wrote:

>
> On Thu, Apr 9, 2015 at 8:41 PM, Derek Homeier <
> derek at astro.physik.uni-goettingen.de> wrote:
>
>> > but if I try to do both, I get the diagonal instead
>> >
>> > >>> a[[1,2],[1,2]]
>> > array([22, 33])
>> >
>> a[1:3,1:3]?
>>
>> Can’t be generalised to arbitrary selections of rows,columns, though
>> (e.g. a[1::2,::2] still works…)
>>
>
> I am interested in the arbitrary selection of rows and columns given by
> indices or by boolean selectors.
>

This is what you are looking for:

a[np.ix_([1, 2], [1, 2])]

Jaime

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