Sort a List of Tuples in Increasing Order by the Last Element in Each Tuple - Python

The task of sorting a list of tuples in Python based on the last element of each tuple is a common task when working with structured data. This involves arranging the tuples in increasing order according to their second or last value, often for easier data analysis or searching. For example, given a list [(1, 3), (3, 2), (2, 1)], sorting by the last element will result in [(2, 1), (3, 2), (1, 3)].

Using sorted()

sorted() is the most efficient way to sort a list of tuples. It allows the use of a key argument with a lambda function to specify that sorting should be done based on the last element of each tuple.

a = [(1, 3), (3, 2), (2, 1)]

res = sorted(a, key=lambda x: x[1])
print(res)

[(2, 1), (3, 2), (1, 3)]

Explanation : sorted() with key=lambda x: x[1] sorts tuples by their second element and sorted list is stored in res .

Using sort()

sort() works similarly to sorted(), but it modifies the original list in place instead of returning a new one. It’s slightly more memory-efficient because it doesn't create a copy.

a = [(1, 3), (3, 2), (2, 1)]

a.sort(key=lambda x: x[1])
print(a)

[(2, 1), (3, 2), (1, 3)]

Explanation:sort() with key=lambda x: x[1] sorts the list a in place based on the second element of each tuple. It modifies the original list instead of creating a new one.

Using itemgetter()

itemgetter() from the operator module can be used instead of a lambda function. It is faster for large datasets because it avoids function call overhead

from operator import itemgetter

a = [(1, 3), (3, 2), (2, 1)]
res = sorted(a, key=itemgetter(1))
print(res)

[(2, 1), (3, 2), (1, 3)]

Explanation: sorted() with key=itemgetter(1) sorts tuples by their second element. itemgetter(1) efficiently retrieves the second element and the sorted result is stored in res.

Using list comprehension

While less common and less readable, list comprehension with enumerate() can also achieve sorting by the last element. This is more of a creative approach, often useful if we need tuple indices as part of the sorting result.

a = [(1, 3), (3, 2), (2, 1)]

res = [x for _, x in sorted(enumerate(a), key=lambda x: x[1][1])]
print(res)

[(2, 1), (3, 2), (1, 3)]

Explanation: enumerate(a) pairs tuples with indices, sorts by the second element using key=lambda x: x[1][1] and list comprehension extracts the sorted tuples into res.