How to Sort Lists by Multiple Attributes in Python?

Sorting Lists by Multiple Attributes: A Comprehensive Guide

Sorting data is a fundamental aspect of many programming tasks. When dealing with complex data structures, it often becomes necessary to sort based on multiple attributes. This article addresses the question of sorting a list of lists based on multiple criteria.

The provided code snippet shows a list of lists, where each inner list represents an object with various attributes. The goal is to sort this list by two attributes: the "tall" or "short" attribute and the color attribute.

Using Itemgetter for Multiple-Criteria Sorting

Itemgetter is a useful function for indexing multiple attributes in a tuple. It takes multiple indices as arguments and returns a function that extracts those attributes from a given tuple. Using itemgetter, you can create a key function that considers both the "tall/short" and the color attribute for sorting:

import operator

s = sorted(s, key = operator.itemgetter(1, 2))

Using Lambda Functions for Key Attribute Selection

Another way to specify a key function for sorting is to use lambda functions. Lambda functions are anonymous functions that can be defined inline. The following lambda function returns a tuple of the "tall/short" and color attributes:

s = sorted(s, key = lambda x: (x[1], x[2]))

Using either of these methods, you can sort the list based on multiple criteria. The result will be a list of lists sorted according to the specified attributes.

Direct Sorting

In the given code snippet, sorted is used to return a new sorted list. However, you can also directly sort the list itself using the sort method. This will modify the original list in place:

s.sort(key = operator.itemgetter(1, 2))

Conclusion

By utilizing itemgetter or lambda functions, you can define key functions to sort lists by multiple attributes. This technique is particularly useful when dealing with complex data structures and can simplify the sorting process.

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