NumPy: Calculate the sum of all columns of a 2D NumPy array

Last update on April 26 2025 12:38:14 (UTC/GMT +8 hours)

Sum all columns of a 2D array.

Write a NumPy program to calculate the sum of all columns in a 2D NumPy array.

Sample Solution:

Python Code:

# Importing the NumPy library and aliasing it as 'np'
import numpy as np

# Generating a NumPy array 'num' containing numbers from 0 to 35 using arange()
num = np.arange(36)

# Reshaping the array 'num' into a 4x9 matrix and assigning it to 'arr1'
arr1 = np.reshape(num, [4, 9])

# Displaying a message indicating the original array will be printed
print("Original array:")

# Printing the original array 'arr1'
print(arr1)

# Computing the sum of each column of the array 'arr1' along axis 0 (columns) and storing it in 'result'
result = arr1.sum(axis=0)

# Displaying a message indicating the sum of all columns will be printed
print("\nSum of all columns:")

# Printing the sum of each column of the array 'arr1'
print(result) 

Sample Output:

Original array:
[[ 0  1  2  3  4  5  6  7  8]
 [ 9 10 11 12 13 14 15 16 17]
 [18 19 20 21 22 23 24 25 26]
 [27 28 29 30 31 32 33 34 35]]

Sum of all columns:
[54 58 62 66 70 74 78 82 86]

Explanation:

This above code demonstrates how to use NumPy to find the sum of elements along the columns of a 2D array.

num = np.arange(36): This code creates a 1D NumPy array called num with elements from 0 to 35.

arr1 = np.reshape(num, [4, 9]): This code reshapes the num array into a 2D array ‘arr1’ with 4 rows and 9 columns.

result = arr1.sum(axis=0): This code calculates the sum of elements along the columns (axis=0) of the 2D array ‘arr1’. The result is a 1D array with the same length as the number of columns in ‘arr1’.

Pictorial Presentation:

For more Practice: Solve these Related Problems:

• Write a NumPy program to compute the column-wise sums of a 2D array and then subtract the overall row sum from each column.
• Create a function that returns both the sum and mean of each column in a given matrix.
• Implement a solution that uses np.sum with axis=0 and then applies a transformation to the summed result.
• Test the column summing operation on an array with negative and positive values to validate the output.

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