How Can I Sort Multiple Lists in Python While Maintaining Alignment?

Sorting Lists While Preserving Alignment

When working with multiple parallel lists, it can be necessary to sort one list while maintaining the corresponding order of elements in the other lists. To achieve this, we present two classic approaches.

The "Decorate, Sort, Undecorate" Idiom

This technique simplifies the task using Python's built-in zip function, which combines elements from multiple lists into tuples:

list1 = [3, 2, 4, 1, 1]
list2 = ['three', 'two', 'four', 'one', 'one2']
list1, list2 = zip(*sorted(zip(list1, list2)))

After sorting the tuples by the first element (list1), the order is applied to both lists.

In-Place Sorting

For increased speed, you can use an in-place sorting approach:

tups = zip(list1, list2)
tups.sort()
result1, result2 = zip(*tups)

This approach typically outperforms the one-line version for small lists but becomes comparable for larger lists due to Python's optimized zip routines.

Alternative Approaches

1. Sorting Indices: If comparing elements of the second list is inefficient or unsupported, sort the indices instead and use them to reorder the lists.
2. Key Function: Define a key function that sorts based on the first list without comparing elements of the second list:

list1 = [3, 2, 4, 1, 1]
list2 = [num * num for num in list1]
result1, result2 = zip(*sorted(zip(list1, list2), key=lambda x: x[0]))

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