numpy.extract(condition, arr)
Return the elements of an array that satisfy some condition.
等价于：extractis equivalent to arr[condition].
Parameters
condition [array_like]
An array whose nonzero or True entries indicate the elements of arr to extract.
arr [array_like]
Returns
extract [ndarray]
Rank 1 array of values from arr where condition is True.
示例
选出除以3余数为0的元素
Input array of the same size as condition.
import numpy as np
arr = np.arange(12).reshape((3, 4))
print(arr)[[ 0 1 2 3][ 4 5 6 7][ 8 9 10 11]]
condition = np.mod(arr, 3)==0
np.extract(condition, arr)array([0, 3, 6, 9])
等价于
arr[np.mod(arr,3)==0]array([0, 3, 6, 9])