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:
Python3
# importing required librariesimport numpy# explicit function to compute column wise sumdef 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 ArrayTwoDList = [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]TwoDArray = numpy.array(TwoDList)# displaying the 2D Arrayprint("2D Array:")print(TwoDArray)# printing the sum of each columnprint("\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 :
Python3
# importing required librariesimport numpy# explicit function to compute column wise sumdef 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 ArrayTwoDList = [[1.2, 2.3], [3.4, 4.5]]TwoDArray = numpy.array(TwoDList)# displaying the 2D Arrayprint("2D Array:")print(TwoDArray)# printing the sum of each columnprint("\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 :
Python3
# importing required librariesimport numpy# creating the 2D ArrayTwoDList = [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]TwoDArray = numpy.array(TwoDList)# displaying the 2D Arrayprint("2D Array:")print(TwoDArray)# printing the sum of each columnprint("\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 :
Python3
# importing required librariesimport numpy# creating the 2D ArrayTwoDList =[[1.2, 2.3], [3.4, 4.5]]TwoDArray = numpy.array(TwoDList)# displaying the 2D Arrayprint("2D Array:")print(TwoDArray)# printing the sum of each columnprint("\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
