Reshuffle numpy array based on indices in a second array

Question

I have 2 numpy arrays:

A = np.array([6, 7 ,8 ,9, 0])
B = np.array([5, 3, 2, 4, 1])

And would like to reshuffle the first one using the second array. So the first element of A should go to place 5 in the output array. The second element should go to to the third etc. So the output array becomes:

C = np.array([0, 8, 7, 9, 6])

This is simple using a simply python loop, but I would like to use numpy only. Speed is very important.

Warren Weckesser · Accepted Answer · 2015-08-10 13:23:10Z

3

Numpy allows you to use B to index A. You have to subtract 1 from B, because indices in numpy arrays begin at 0:

In [17]: A = np.array([6, 7, 8, 9, 0])

In [18]: B = np.array([5, 3, 2, 4, 1])

In [19]: C = A[B-1]

In [20]: C
Out[20]: array([0, 8, 7, 9, 6])

edited Aug 10, 2015 at 13:23

answered Aug 10, 2015 at 13:15

Warren Weckesser

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