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Next Article:
Python - Sort List items on basis of their Digits
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Sort List of Lists Ascending and then Descending in Python

Last Updated : 15 Jan, 2025
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Sorting a list of lists in Python can be done in many ways, we will explore the methods to achieve the same in this article.

Using sorted() with a key

sorted() function is a flexible and efficient way to sort lists. It creates a new list while leaving the original unchanged.

Python 
a = [[1, 2, 3], [3, 2, 1], [2, 3, 1]]  # Sort in ascending order based on the first element asc = sorted(a, key=lambda x: x[0]) print(asc)     # Sort in descending order based on the first element desc = sorted(a, key=lambda x: x[0], reverse=True) print(desc)

Output
[[1, 2, 3], [2, 3, 1], [3, 2, 1]] [[3, 2, 1], [2, 3, 1], [1, 2, 3]]

Explanation:

  • Key parameter is used to specify the sorting criterion (in this case, the first element).
  • Reverse parameter is used for descending order sorting.

Let's explore some more methods and see how we can sort list of lists in ascending then descending order in Python.

Table of Content

  • Using sort() method
  • Using itemgetter() from operator module
  • Using a custom comparator

Using sort() method

sort() method sorts the list in place, making it memory efficient when a new list is unnecessary.

Python 
a = [[1, 2, 3], [3, 2, 1], [2, 3, 1]]  # Sort in ascending order based on the first element a.sort(key=lambda x: x[0]) print(a)   # Sort in descending order based on the first element a.sort(key=lambda x: x[0], reverse=True) print(a)

Output
[[1, 2, 3], [2, 3, 1], [3, 2, 1]] [[3, 2, 1], [2, 3, 1], [1, 2, 3]]

Explanation: This method modifies the original list, saving memory as no new list is created.

Using itemgetter() from operator module

itemgetter() function from the operator module is another efficient way to sort lists, especially for readability.

Python 
from operator import itemgetter  a = [[1, 2, 3], [3, 2, 1], [2, 3, 1]]  # Sort in ascending order based on the first element asc = sorted(a, key=itemgetter(0)) print(asc)  # Sort in descending order based on the first element desc = sorted(a, key=itemgetter(0), reverse=True) print(desc)

Output
[[1, 2, 3], [2, 3, 1], [3, 2, 1]] [[3, 2, 1], [2, 3, 1], [1, 2, 3]]

Explanation: itemgetter() function simplifies accessing specific indices in the list, making the code more readable.

Using a custom comparator

We can use a custom comparator with the functools.cmp_to_key() function to define complex sorting behavior.

Python 
from functools import cmp_to_key a = [[1, 2, 3], [3, 2, 1], [2, 3, 1]]  # Custom comparator function def compare(x, y):     return x[0] - y[0]  # Sort in ascending order based on the first element asc = sorted(a, key=cmp_to_key(compare)) print(asc)

Output
[[1, 2, 3], [2, 3, 1], [3, 2, 1]]

Explanation: Custom comparator function allows for more complex sorting criteria but is generally slower than using a key.


Next Article
Python - Sort List items on basis of their Digits

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Article Tags :
  • Python
  • Python Programs
  • python-list
  • python sorting-exercises
Practice Tags :
  • python
  • python-list

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