python numpy 数组中元素大于等于0的元素

 >>> import numpy as np
 >>> a = np.random.randint(-5, 5, (5, 5))
 >>> a
 array([[-4, -4, -5,  2,  1],
        [-1, -2, -1,  3,  3],
        [-1, -2,  3, -5,  3],
        [ 0, -3, -5,  1, -4],
        [ 0,  3,  1,  3, -4]])
 # 方式一
 >>> np.maximum(a, 0)
 array([[0, 0, 0, 2, 1],
        [0, 0, 0, 3, 3],
        [0, 0, 3, 0, 3],
        [0, 0, 0, 1, 0],
        [0, 3, 1, 3, 0]])
 # 方式二
 >>> (a + abs(a)) / 2
 array([[0, 0, 0, 2, 1],
        [0, 0, 0, 3, 3],
        [0, 0, 3, 0, 3],
        [0, 0, 0, 1, 0],
        [0, 3, 1, 3, 0]])
 # 方式三
 >>> b = a.copy()
 >>> b[b < 0] = 0
 >>> b
 array([[0, 0, 0, 2, 1],
        [0, 0, 0, 3, 3],
        [0, 0, 3, 0, 3],
        [0, 0, 0, 1, 0],
        [0, 3, 1, 3, 0]])
 # 方式四
 >>> np.where(a > 0, a, 0)
 array([[0, 0, 0, 2, 1],
        [0, 0, 0, 3, 3],
        [0, 0, 3, 0, 3],
        [0, 0, 0, 1, 0],
        [0, 3, 1, 3, 0]])