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Calculate the sum of all columns in a 2D NumPy array
  • Last Updated : 19 Aug, 2020
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Let us see how to calculate the sum of all the columns in a 2D NumPy array.

Method 1 : Using a nested loop to access the array elements column-wise and then storing their sum in a variable and then printing it.

Example 1:




# importing required libraries
import numpy
  
# explicit function to compute column wise sum 
def colsum(arr, n, m):
    for i in range(n):
        su = 0;
        for j in range(m):
            su += arr[j][i]
        print(su, end = " ")    
  
# creating the 2D Array
TwoDList = [[1, 2, 3], [4, 5, 6], 
            [7, 8, 9], [10, 11, 12]]
TwoDArray = numpy.array(TwoDList)
  
# displaying the 2D Array
print("2D Array:")
print(TwoDArray)
  
# printing the sum of each column
print("\nColumn-wise Sum:")
colsum(TwoDArray, len(TwoDArray[0]), len(TwoDArray))

Output :

2D Array:
[[ 1  2  3]
 [ 4  5  6]
 [ 7  8  9]
 [10 11 12]]

Column-wise Sum:
22 26 30 

Example 2 :






# imporing required libraries
import numpy
  
# explicit function to compute column wise sum 
def colsum(arr, n, m):
    for i in range(n):
        su = 0;
        for j in range(m):
            su += arr[j][i]
        print(su, end = " ")    
  
# creating the 2D Array
TwoDList = [[1.2, 2.3], [3.4, 4.5]]
TwoDArray = numpy.array(TwoDList)
  
# displaying the 2D Array
print("2D Array:")
print(TwoDArray)
  
# printing the sum of each column
print("\nColumn-wise Sum:")
colsum(TwoDArray, len(TwoDArray[0]), len(TwoDArray))

Output :

2D Array:
[[1.2 2.3]
 [3.4 4.5]]

Column-wise Sum:
4.6 6.8 

Method 2: Using the sum() function in NumPy, numpy.sum(arr, axis, dtype, out) function returns the sum of array elements over the specified axis. To compute the sum of all columns the axis argument should be 0 in sum() function.

Example 1 :




# importing required libraries
import numpy
  
# creating the 2D Array
TwoDList = [[1, 2, 3], [4, 5, 6], 
            [7, 8, 9], [10, 11, 12]]
TwoDArray = numpy.array(TwoDList)
  
# displaying the 2D Array
print("2D Array:")
print(TwoDArray)
  
# printing the sum of each column
print("\nColumn-wise Sum:")
print(numpy.sum(TwoDArray, axis = 0))

Output :

2D Array:
[[ 1  2  3]
 [ 4  5  6]
 [ 7  8  9]
 [10 11 12]]

Column-wise Sum:
22 26 30

Example 2 :




# importing required libraries
import numpy
  
# creating the 2D Array
TwoDList =[[1.2, 2.3], [3.4, 4.5]]
TwoDArray = numpy.array(TwoDList)
  
# displaying the 2D Array
print("2D Array:")
print(TwoDArray)
  
# printing the sum of each column
print("\nColumn-wise Sum:")
print(*numpy.sum(TwoDArray, axis = 0))

Output :

2D Array:
[[1.2 2.3]
 [3.4 4.5]]

Column-wise Sum:
4.6 6.8

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