How to get N maximum values of each array from a numpy array of arrays

Question

I have a numpy array of arrays x = [[1, 3, 4, 5], [6, 2, 5, 7]]. I want to get N maximum values from each array of the numpy array: [[5, 4], [7, 6]]. I have tried using np.argpartition(x, -N, axis=0)[-N:] but it gives ValueError: kth(=-3) out of bounds (1). What is the efficient way for doing this?

Answer 1

You can do this by sorting each row and slicing as you want:

np.sort(x, axis=1)[:, :2]  # --> [[1 3] [2 5]]    2 minimum in each row
np.sort(x, axis=1)[:, 2:]  # --> [[4 5] [6 7]]    2 maximum in each row