numpy array boolean index true false code example

Example 1: python numpy array boolean indexing

x = np.array([1., -1., -2., 3])
x[x < 0] = 20
x

Output:
array([  1.,  20.,  20.,   3.])

Example 2: numpy boolean array

arr_1 = np.random.randn(3, 3)
arr_2 = np.random.randn(3, 3)

bool_arr = arr_1 < 0.5    
print(bool_arr.dtype)
# output: bool

bool_arr = arr_1 < arr_2
print(bool_arr.dtype)
# output: bool