Sort a list of tuples by the Nth tuple element in Python

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Borislav Hadzhiev

Last updated: Jun 29, 2022

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Sort a list of tuples by the Nth tuple element in Python #

Use the key argument of the sorted() function to sort a list of tuples by the Nth element, e.g. sorted_list = sorted(list_of_tuples, key=lambda t: t[0]). The function will return a new list, sorted by the tuple element at the specified index.

main.py
list_of_tuples = [(2, 44), (3, 22), (1, 33)] # ✅ sort list of tuples by first element (ascending order) sorted_list = sorted( list_of_tuples, key=lambda t: t[0] ) # 👇️ [(1, 33), (2, 44), (3, 22)] print(sorted_list) # ---------------------------------------------------------- # ✅ sort list of tuples by first element (descending order) sorted_list_desc = sorted( list_of_tuples, key=lambda t: t[0], reverse=True ) # 👇️ [(3, 22), (2, 44), (1, 33)] print(sorted_list_desc)

The sorted function takes an iterable and returns a new sorted list from the items in the iterable.

The function takes an optional key argument that can be used to sort by different criteria.
main.py
list_of_tuples = [(2, 44), (3, 22), (1, 33)] sorted_list = sorted(list_of_tuples, key=lambda t: t[0]) # 👇️ [(1, 33), (2, 44), (3, 22)] print(sorted_list)

The example sorts the list of tuples by the first (index 0) element in each tuple.

Python indexes are zero-based. The first item in a tuple has an index of 0, the second an index of 1, etc.

The key argument can be set to a function that determines the sorting criteria.

If you need to sort the list of tuples by the Nth element in descending order (greatest to lowest), set the reverse argument to true when calling sorted().

main.py
list_of_tuples = [(2, 44), (3, 22), (1, 33)] sorted_list_desc = sorted( list_of_tuples, key=lambda t: t[0], reverse=True ) # 👇️ [(3, 22), (2, 44), (1, 33)] print(sorted_list_desc)
If the reverse argument is set to True, then the elements are sorted as if each comparison were reversed.

If you need to sort by another element, adjust the index accessor in the lambda function.

Here is an example that sorts the list of tuples by the third (index 2) item in each tuple.

main.py
list_of_tuples = [(2, 44, 100), (3, 22, 25), (1, 33, 50)] sorted_list = sorted( list_of_tuples, key=lambda t: t[2] ) # # 👇️ [(3, 22, 25), (1, 33, 50), (2, 44, 100)] print(sorted_list)

Instead of using a lambda function, you can also use the operator.itemgetter() method to specify the index you want to sort by.

main.py
from operator import itemgetter list_of_tuples = [(2, 44), (3, 22), (1, 33)] sorted_list = sorted( list_of_tuples, key=itemgetter(0) ) # # 👇️ [(1, 33), (2, 44), (3, 22)] print(sorted_list)

The operator.itemgetter method returns a callable object that fetches the item at the specified index.

For example, x = itemgetter(0) and then calling x(my_tuple), returns my_tuple[0].

Using the itemgetter method is faster than using a lambda function, but it is also a bit more implicit.

Alternatively, you can use the list.sort() method to sort the list of tuples by the Nth element in place.

main.py
from operator import itemgetter list_of_tuples = [(2, 44), (3, 22), (1, 33)] list_of_tuples.sort(key=itemgetter(0)) # # 👇️ [(1, 33), (2, 44), (3, 22)] print(list_of_tuples)

The list.sort method sorts the list in place and it uses only < comparisons between items.

The method takes the following 2 keyword-only arguments:

NameDescription
keya function that takes 1 argument and is used to extract a comparison key from each list element
reversea boolean value indicating whether each comparison should be reversed

Note that the list.sort method mutates the list in place and returns None.

You can use the sorted() function if you need a new list instance rather than an in-place mutation.

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