>>> import numpy as np
>>> a = np.random.randint(0,20,10)
>>> a
array([ 6,  5,  7,  4, 11, 11, 15,  7,  2, 11])
>>> mask = (a%2==0)
>>> mask
array([ True, False, False,  True, False, False, False, False,  True,
       False])
>>> a[mask]
array([6, 4, 2])
>>> b = a[mask]
>>> b
array([6, 4, 2])
>>> a[mask] = -1
>>> a
array([-1,  5,  7, -1, 11, 11, 15,  7, -1, 11])
>>> np.shares_memory(a,a[mask])
False
>>>