Sort a list of tuples in Python

Sort a list of tuples in Python #

Use the key argument of the sorted() function to sort a list of tuples, e.g. sorted_list = sorted(list_of_tuples, key=lambda t: t[1]). The function will sort the list of tuples by the tuple element at the specified index.

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list_of_tuples = [(1, 100), (2, 50), (3, 75)]

# ✅ sort list of tuples by element at index (ascending order)
sorted_list = sorted(list_of_tuples, key=lambda t: t[1])

print(sorted_list)  # 👉️ [(2, 50), (3, 75), (1, 100)]

# ----------------------------------------------------

# ✅ sort list of tuples by element at index in descending order

sorted_list_descending = sorted(
    list_of_tuples,
    key=lambda t: t[1],
    reverse=True
)

# 👇️ [(1, 100), (3, 75), (2, 50)]
print(sorted_list_descending)

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

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list_of_tuples = [(1, 100), (2, 50), (3, 75)]

sorted_list = sorted(list_of_tuples, key=lambda t: t[1])

print(sorted_list)  # 👉️ [(2, 50), (3, 75), (1, 100)]

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

The example sorts the list of tuples by the second item (index 1) in each tuple.

If you need to sort the list of tuples in descending (greatest to lowest), set the reverse argument to true in the call to the sorted() function.

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list_of_tuples = [(1, 100), (2, 50), (3, 75)]

sorted_list_descending = sorted(
    list_of_tuples,
    key=lambda t: t[1],
    reverse=True
)

# 👇️ [(1, 100), (3, 75), (2, 50)]
print(sorted_list_descending)

You can also use this approach to sort a list of tuples by multiple indexes.

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list_of_tuples = [(1, 3,  100), (2, 3,  50), (3, 2, 75)]

# ✅ sort list of tuples by second and third elements
sorted_list = sorted(
  list_of_tuples,
  key=lambda t: (t[1], t[2])
)

print(sorted_list)  # 👉️ [(3, 2, 75), (2, 3, 50), (1, 3, 100)]

The example sorts the list of tuples by the elements at index 1 and 2 in each tuple.

Since the second item in the third tuple is the lowest, it gets moved to the front.

An alternative to using a lambda function is to use the operator.itemgetter() method to specify the index you want to sort by.

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from operator import itemgetter

list_of_tuples = [(1, 100), (2, 50), (3, 75)]


sorted_list = sorted(list_of_tuples, key=itemgetter(1))

print(sorted_list)  # 👉️ [(2, 50), (3, 75), (1, 100)]

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

For example, x = itemgetter(1) and then calling x(my_tuple), returns my_tuple[1].

You can also use this approach to sort by multiple indices.

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from operator import itemgetter

list_of_tuples = [(1, 3,  100), (2, 3,  50), (3, 2, 75)]

# ✅ sort list of tuples by second and third elements
sorted_list = sorted(list_of_tuples, key=itemgetter(1, 2))

print(sorted_list)  # 👉️ [(3, 2, 75), (2, 3, 50), (1, 3, 100)]

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.

Use the key argument of the list.sort() method to sort a list of tuples in place, e.g. list_of_tuples.sort(key=lambda t: t[1]). The list.sort() method will sort the list of tuples by the tuple element at the specified index.

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list_of_tuples = [(1, 100), (2, 50), (3, 75)]

list_of_tuples.sort(key=lambda t: t[1])

print(list_of_tuples)  # 👉️ [(2, 50), (3, 75), (1, 100)]

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:

The other keyword argument the sort method takes is reverse.

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list_of_tuples = [(1, 100), (2, 50), (3, 75)]

list_of_tuples.sort(key=lambda t: t[1], reverse=True)

print(list_of_tuples)  # 👉️ [(1, 100), (3, 75), (2, 50)]

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.