`numpy:flatnonzero`

Signature

def flatnonzero(a)

Return indices that are non-zero in the flattened version of a.

This is equivalent to np.nonzero(np.ravel(a))[0].

res : ndarray: Output array, containing the indices of the elements of a.ravel() that are non-zero.

import numpy as np
x = np.arange(-2, 3)
x
np.flatnonzero(x)

✓

array([0, 1, 3, 4])

Use the indices of the non-zero elements as an index array to extract these elements:

x.ravel()[np.flatnonzero(x)]

✓

array([-2, -1,  1,  2])