Calculate the mean across dimension in a 2D NumPy array

Calculating the sum of all columns of a 2D NumPy array

Last Updated : 02 Sep, 2020

Let us see how to calculate the sum of all the columns of a 2 dimensional NumPy array. Example :

Input : 
[[1, 2, 3, 4, 5],
 [5, 6, 7, 8, 9],
 [2, 1, 5, 7, 8],
 [2, 9, 3, 1, 0]]
         
Output :  [10, 18, 18, 20, 22]

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

Output : [8, 15, 12, 18]

Approach 1 : We will be using the sum() method. We will pass parameter axis = 0 to get the sum columns wise.

python3

# 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)

Output :

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

Approach 2 : We can also use the numpy.einsum() method, with parameter 'ij->j'.

Python3

# 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)

Output :

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

Calculate the mean across dimension in a 2D NumPy array

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