计算一个二维NumPy数组所有列的总和

让我们看看如何计算一个2维NumPy数组的所有列的总和。

示例 :

输入:

[[1, 2, 3, 4, 5],
 [5, 6, 7, 8, 9],
 [2, 1, 5, 7, 8],
 [2, 9, 3, 1, 0]]

输出:

 [10, 18, 18, 20, 22]

输入:

[[5, 4, 1, 7],
 [0, 9, 3, 5], 
 [3, 2, 8, 6]]

输出:

[8, 15, 12, 18]

方法1：我们将使用sum()方法。我们将传递参数axis = 0，以获得按列计算的总和。

# importing numpy
import numpy as np
  
# initialize the 2-d array
arr = np.array([[1, 2, 3, 4, 5],
                [5, 6, 7, 8, 9],
                [2, 1, 5, 7, 8],
                [2, 9, 3, 1, 0]])
  
# calculating column wise sum
sum_2d = arr.sum(axis = 0)
  
# displaying the sum
print("Column wise sum is :\n", sum_2d)

输出 :

Column wise sum is :
 [10 18 18 20 22]

方法2 :我们也可以使用numpy.einsum()方法，参数为’ij->j’。

# importing numpy
import numpy as np
  
# initialize the 2-d array
arr = np.array([[1, 2, 3, 4, 5],
                [5, 6, 7, 8, 9],
                [2, 1, 5, 7, 8],
                [2, 9, 3, 1, 0]])
  
# calculating column wise sum
sum_2d = np.einsum('ij->j', arr)
  
# displaying the sum
print("Column wise sum is :\n", sum_2d)