Sort a list according to the second element of sublist - Python
Last Updated :
09 May, 2025
Sorting a list by the second element of each sublist means rearranging the sublists based on the value at index 1. For example, given the list [[1, 3], [2, 1], [4, 2], [3, 5]], sorting by the second element results in [[2, 1], [4, 2], [1, 3], [3, 5]], where the second elements (1, 2, 3, 5) are in ascending order. Let's explore various methods to achieve this efficiently.
Using itemgetter()
itemgetter() function from Python’s operator module is a highly efficient way to sort lists when dealing with sublists or tuples. It avoids the overhead of defining a lambda function, making it ideal for larger datasets.
Python
from operator import itemgetter
a = [[1, 3], [2, 1], [4, 2], [3, 5]]
a = sorted(a, key=itemgetter(1))
print(a)
Output[[2, 1], [4, 2], [1, 3], [3, 5]]
Explanation: sorted(a, key=itemgetter(1)) sorts the list a based on the second element of each sublist. The itemgetter(1) function specifies that the sorting should use the value at index 1 of each sublist.
Using sorted()
sorted() function returns a new sorted list from the given iterable. When combined with a lambda, it allows custom sorting logic such as sorting by the second element.
Python
a = [[1, 3], [2, 1], [4, 2], [3, 5]]
a = sorted(a, key=lambda x: x[1])
print(a)
Output[[2, 1], [4, 2], [1, 3], [3, 5]]
Explanation: sorted(a, key=lambda x: x[1]) sorts the list a by the second element of each sublist, using a lambda function to specify that the sorting should be done based on the value at index 1 of each sublist.
Using sort() Method
If we don’t need a new list and prefer to sort the list in place, we can use the sort() method. It directly modifies the list we’re working with instead of creating a new one.
Python
a = [[1, 3], [2, 1], [4, 2], [3, 5]]
a.sort(key=lambda x: x[1])
print(a)
Output[[2, 1], [4, 2], [1, 3], [3, 5]]
Explanation: a.sort(key=lambda x: x[1]) sorts the list a in place by the second element of each sublist. The lambda function specifies that the sorting should be done based on the value at index 1 of each sublist.
Using loop
If you want to sort the list without using any built-in sorting functions, you can implement a basic Bubble Sort algorithm or any other sorting logic manually. This is useful for learning purposes or in environments where inbuilt functions are restricted.
Python
a = [[1, 3], [2, 1], [4, 2], [3, 5]]
n = len(a)
for i in range(n):
for j in range(0, n-i-1):
if a[j][1] > a[j+1][1]:
a[j], a[j+1] = a[j+1], a[j]
print(a)
Output[[2, 1], [4, 2], [1, 3], [3, 5]]
Explanation: Outer loop runs n times, bubbling the largest second element up each pass. The inner loop compares adjacent sublists, skipping the last i sorted elements. If a[j][1] > a[j+1][1], the sublists are swapped, moving the larger element toward the end.
Related Articles
Similar Reads
Python Tutorial - Learn Python Programming Language Python is one of the most popular programming languages. Itâs simple to use, packed with features and supported by a wide range of libraries and frameworks. Its clean syntax makes it beginner-friendly. It'sA high-level language, used in web development, data science, automation, AI and more.Known fo
10 min read
Python Interview Questions and Answers Python is the most used language in top companies such as Intel, IBM, NASA, Pixar, Netflix, Facebook, JP Morgan Chase, Spotify and many more because of its simplicity and powerful libraries. To crack their Online Assessment and Interview Rounds as a Python developer, we need to master important Pyth
15+ min read
Python OOPs Concepts Object Oriented Programming is a fundamental concept in Python, empowering developers to build modular, maintainable, and scalable applications. By understanding the core OOP principles (classes, objects, inheritance, encapsulation, polymorphism, and abstraction), programmers can leverage the full p
11 min read
Python Projects - Beginner to Advanced Python is one of the most popular programming languages due to its simplicity, versatility, and supportive community. Whether youâre a beginner eager to learn the basics or an experienced programmer looking to challenge your skills, there are countless Python projects to help you grow.Hereâs a list
10 min read
Python Exercise with Practice Questions and Solutions Python Exercise for Beginner: Practice makes perfect in everything, and this is especially true when learning Python. If you're a beginner, regularly practicing Python exercises will build your confidence and sharpen your skills. To help you improve, try these Python exercises with solutions to test
9 min read
Python Programs Practice with Python program examples is always a good choice to scale up your logical understanding and programming skills and this article will provide you with the best sets of Python code examples.The below Python section contains a wide collection of Python programming examples. These Python co
11 min read
Python Introduction Python was created by Guido van Rossum in 1991 and further developed by the Python Software Foundation. It was designed with focus on code readability and its syntax allows us to express concepts in fewer lines of code.Key Features of PythonPythonâs simple and readable syntax makes it beginner-frien
3 min read
Python Data Types Python Data types are the classification or categorization of data items. It represents the kind of value that tells what operations can be performed on a particular data. Since everything is an object in Python programming, Python data types are classes and variables are instances (objects) of thes
9 min read
Input and Output in Python Understanding input and output operations is fundamental to Python programming. With the print() function, we can display output in various formats, while the input() function enables interaction with users by gathering input during program execution. Taking input in PythonPython input() function is
8 min read
Enumerate() in Python enumerate() function adds a counter to each item in a list or other iterable. It turns the iterable into something we can loop through, where each item comes with its number (starting from 0 by default). We can also turn it into a list of (number, item) pairs using list().Let's look at a simple exam
3 min read