How to Sort a List of Tuples by the Second Item in Python?

Sorting Tuples by Second Item: A Comprehensive Guide

Sorting data structures effectively is a crucial aspect of programming, and understanding how to sort tuples by their second item is essential. This article addresses this precise question, providing a detailed walkthrough and comprehensive answers based on a real-world scenario.

The Question

Consider a list of tuples with the following structure:

[('abc', 121), ('abc', 231), ('abc', 148), ('abc', 221)]

The objective is to sort this list in ascending order based on the integer values (second item) within each tuple.

The Solution

The key to sortingtuples by the second item lies in utilizing the sorted() function's key keyword argument. By default, sorted() sorts in increasing order, which is precisely what we seek. Here's how to implement it:

sorted(
    [('abc', 121), ('abc', 231), ('abc', 148), ('abc', 221)],
    key=lambda x: x[1]
)

The key argument is an essential aspect of this solution. It defines a function that specifies how to extract the comparable element from each tuple. In this case, we want to compare the second item of each tuple, which is accessed via x[1].

Optimization

For improved performance, one can consider using operator.itemgetter(1) instead of lambda x: x[1] as the key argument. This is because operator.itemgetter(1) is significantly faster and more concise. The updated code:

sorted(
    [('abc', 121), ('abc', 231), ('abc', 148), ('abc', 221)],
    key=operator.itemgetter(1)
)

Conclusion

Sorting tuples by the second item is straightforward using Python's sorting capabilities. By understanding how to use the key argument effectively, programmers can efficiently sort data structures based on specific criteria. This article provides both a straightforward solution and an optimized approach, enabling developers to make informed decisions based on their specific performance requirements.

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