NumPy: Sort an given array by the n^th column

Last update on August 30 2025 12:29:02 (UTC/GMT +8 hours)

9. Sort Array by Nth Column

Write a NumPy program to sort an given array by the n^th column.

Sample Solution:

Python Code:

# Importing the NumPy library
import numpy as np

# Displaying a message indicating the original array is going to be printed
print("Original array:\n")

# Generating a 3x3 array of random integers from 0 to 10
nums = np.random.randint(0, 10, (3, 3))

# Displaying the original array
print(nums)

# Displaying a message indicating sorting the array by the nth column
print("\nSort the said array by the nth column: ")

# Sorting the array by the values in the nth column using argsort
print(nums[nums[:, 1].argsort()]) 

Sample Output:

Original array:

[[1 5 0]
 [3 2 5]
 [8 7 6]]

Sort the said array by the nth column: 
[[3 2 5]
 [1 5 0]
 [8 7 6]]

Explanation:

In the above exercise –

nums = np.random.randint(0, 10, (3, 3)): This line creates a 3x3 NumPy array nums containing random integers from 0 (inclusive) to 10 (exclusive).

nums[:, 1]: This line slices the array nums to select all rows and the second column (index 1). The result is a 1D array containing the second column's elements.

nums[:, 1].argsort(): This line uses the argsort() function to obtain the indices that would sort the 1D array containing the elements of the second column.

print(nums[nums[:, 1].argsort()]): This line prints the result of indexing the original nums array using the sorted indices obtained in the previous step. This results in a new array where rows are sorted based on the values in the second column.

For more Practice: Solve these Related Problems:

• Sort a 2D array by the values in its nth column using np.argsort and advanced indexing to reorder rows.
• Create a function that takes a 2D array and a column index as input, then returns the array sorted by that column.
• Implement a solution that first extracts the nth column, sorts it, and uses the sorted indices to rearrange the entire array.
• Test the sorting function on arrays with multiple columns to verify that sorting by the nth column produces the expected ordering.

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• NumPy Sorting and Searching Exercises Home ↩
• NumPy Exercises Home ↩

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