在numpy矩阵中令小于0的元素改为0的实例

>>> import numpy as np>>> a = np.random.randint(-5, 5, (5, 5))>>> aarray([[-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)) / 2array([[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>>> barray([[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]])