python numpy array from index array

Question

I have a 3d array a = np.arange(108).reshape(6, 6, 3). I want to grab certain indices of the array, as defined by i = np.array([[0, 1], [1, 3], [2, 1]]) such that the result is [[3, 4, 5], [27, 28, 29], [39, 40, 41]]. I need an efficient way to do this, as my actual arrays are significantly larger.

akuiper · Accepted Answer · 2018-01-23 04:10:01Z

2

Extract the first and second dimension indices from i, then use advanced indexing:

a[i[:,0], i[:,1], :]   # or a[i[:,0], i[:,1]]

#array([[ 3,  4,  5],
#       [27, 28, 29],
#       [39, 40, 41]])

answered Jan 23, 2018 at 4:10

akuiper

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