`numpy:extract`

Signature

def extract(condition, arr)

Return the elements of an array that satisfy some condition.

This is equivalent to np.compress(ravel(condition), ravel(arr)). If condition is boolean np.extract is equivalent to arr[condition].

Note that place does the exact opposite of extract.

condition : array_like: An array whose nonzero or True entries indicate the elements of arr to extract.
arr : array_like: Input array of the same size as condition.

extract : ndarray: Rank 1 array of values from arr where condition is True.

import numpy as np
arr = np.arange(12).reshape((3, 4))
arr
condition = np.mod(arr, 3)==0
condition
np.extract(condition, arr)

✓

array([0, 3, 6, 9])

If `condition` is boolean:

arr[condition]

✓

array([0, 3, 6, 9])