Sort numpy.array rows by indices

Question

I have 2D numpy.array and a tuple of indices:

a = array([[0, 0], [0, 1], [1, 0], [1, 1]])
ix = (2, 0, 3, 1)

How can I sort array's rows by the indices? Expected result:

array([[1, 0], [0, 0], [1, 1], [0, 1]])

I tried using numpy.take, but it works as I expect only with 1D arrays.

NPE · Accepted Answer · 2014-09-06 11:53:40Z

6

You can in fact use ndarray.take() for this. The trick is to supply the second argument (axis):

>>> a.take(ix, 0)
array([[1, 0],
       [0, 0],
       [1, 1],
       [0, 1]])

(Without axis, the array is flattened before elements are taken.)

Alternatively:

>>> a[ix, ...]
array([[1, 0],
       [0, 0],
       [1, 1],
       [0, 1]])

answered Sep 6, 2014 at 11:40

NPE

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1 Comment

Thank you! I didn't know about the second argument of numpy.take.