How Can I Efficiently Sort a List Based on Multiple Attributes in Python?

Multi-Attribute List Sorting

Sorting a list based on a single attribute is straightforward. However, when multiple attributes dictate the sort order, a more complex approach is required.

Consider the following list of lists:

[[12, 'tall', 'blue', 1],
[2, 'short', 'red', 9],
[4, 'tall', 'blue', 13]]

Sorting this list solely by the 'tall' or 'short' attribute can be achieved using sorted(s, key = itemgetter(1)). However, if the sort order must be based on both the height and color attributes, a more efficient solution is necessary.

Multi-Attribute Key Functions

To sort a list by multiple attributes, a key function can be defined that returns a tuple representing the desired sort order. For instance, the following key function sorts by height first and then by color:

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

Using this key function, the list can be sorted as follows:

s = sorted(s, key=key)

Alternatively, itemgetter() can be employed to achieve the same result more efficiently:

import operator
key = operator.itemgetter(1, 2)

This key function is both faster and does not involve a Python function call.

Direct Sorting

Finally, the above approach can be simplified further by using the sort() method instead of sorted() and reassigning. This eliminates the need to create a new list:

s.sort(key=key)

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