[FIXED] Get elements from a numpy array using another array

Issue

I have a numpy array, a, of shape (2, 5, 2). I need to get 2 elements from the array at locations [0, 1, 0] and [1, 3, 0]. To retrieve these elements, I have an array, b, with entries [1, 3]. When I use a[:,b], I get 2x2 matrix (as expected). How can I change the indexing to return the required vector instead? Following is an MWE.

import numpy as np

a = np.random.randn(2, 5, 2)
b = np.random.randint(0, 5, 2)

c = a[:, b]
c.shape  # prints (2, 2), while I only need a[0, b[0]] and a[1, b[1]].

PS: This problem can be solved using a for loop. However in my actual code the index is in the order of 1000 and therefore not feasible.

Solution

As pointed out in the comments, one can do c = a[np.arange(a.shape[0]), b] to obtain the required result.

Answered By - learner