How do I get indices of N maximum values in a NumPy array?

Question

NumPy proposes a way to get the index of the maximum value of an array via np.argmax.

I would like a similar thing, but returning the indexes of the

Answer 1

If you don't care about the order of the K-th largest elements you can use argpartition, which should perform better than a full sort through argsort.

K = 4 # We want the indices of the four largest values
a = np.array([0, 8, 0, 4, 5, 8, 8, 0, 4, 2])
np.argpartition(a,-K)[-K:]
array([4, 1, 5, 6])

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I ran a few tests and it looks like argpartition outperforms argsort as the size of the array and the value of K increase.