[Numpy-discussion] Right way to do fancy indexing from argsort() result?

[Eric Wieser]

https://github.com/numpy/numpy/issues/8708 is a proposal to add such a
function, with an implementation in https://github.com/numpy/numpy/pull/8714


Eric

On Mon, 26 Mar 2018 at 11:35 Benjamin Root <ben.v.root at gmail.com> wrote:

> Ah, yes, I should have thought about that. Kind of seems like something
> that we could make `np.take()` do, somehow, for something that is easier to
> read.
>
> Thank you!
> Ben Root
>
>
> On Mon, Mar 26, 2018 at 2:28 PM, Robert Kern <robert.kern at gmail.com>
> wrote:
>
>> On Mon, Mar 26, 2018 at 11:24 AM, Benjamin Root <ben.v.root at gmail.com>
>> wrote:
>> >
>> > I seem to be losing my mind... I can't seem to get this to work right.
>> >
>> > I have a (N, k) array `distances` (along with a bunch of other arrays
>> of the same shape). I need to resort the rows, so I do:
>> >
>> > indexs = np.argsort(distances, axis=1)
>> >
>> > How do I use this index array correctly to get back distances sorted
>> along rows? Note, telling me to use `np.sort()` isn't going to work because
>> I need to apply the same indexing to a couple of other arrays.
>> >
>> > new_dists = distances[indexs]
>> >
>> > gives me a (N, k, k) array, while
>> >
>> > new_dists = np.take(indexs, axis=1)
>> >
>> > gives me a (N, N, k) array.
>> >
>> > What am I missing?
>>
>> Broadcasting!
>>
>>   new_dists = distances[np.arange(N)[:, np.newaxis], indexs]
>>
>> --
>> Robert Kern
>>
>> _______________________________________________
>> NumPy-Discussion mailing list
>> NumPy-Discussion at python.org
>> https://mail.python.org/mailman/listinfo/numpy-discussion
>>
>>
> _______________________________________________
> NumPy-Discussion mailing list
> NumPy-Discussion at python.org
> https://mail.python.org/mailman/listinfo/numpy-discussion
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/numpy-discussion/attachments/20180326/10a3502b/attachment.html>