Fix Python – Permutations between two lists of unequal length

Question

Asked By – user1735075

I’m having trouble wrapping my head around a algorithm I’m try to implement. I have two lists and want to take particular combinations from the two lists.

Here’s an example.

names = ['a', 'b']
numbers = [1, 2]

the output in this case would be:

[('a', 1), ('b', 2)]
[('b', 1), ('a', 2)]

I might have more names than numbers, i.e. len(names) >= len(numbers). Here’s an example with 3 names and 2 numbers:

names = ['a', 'b', 'c']
numbers = [1, 2]

output:

[('a', 1), ('b', 2)]
[('b', 1), ('a', 2)]
[('a', 1), ('c', 2)]
[('c', 1), ('a', 2)]
[('b', 1), ('c', 2)]
[('c', 1), ('b', 2)]

Now we will see solution for issue: Permutations between two lists of unequal length


Answer

Note: This answer is for the specific question asked above. If you are here from Google and just looking for a way to get a Cartesian product in Python, itertools.product or a simple list comprehension may be what you are looking for – see the other answers.


Suppose len(list1) >= len(list2). Then what you appear to want is to take all permutations of length len(list2) from list1 and match them with items from list2. In python:

import itertools
list1=['a','b','c']
list2=[1,2]

[list(zip(x,list2)) for x in itertools.permutations(list1,len(list2))]

Returns

[[('a', 1), ('b', 2)], [('a', 1), ('c', 2)], [('b', 1), ('a', 2)], [('b', 1), ('c', 2)], [('c', 1), ('a', 2)], [('c', 1), ('b', 2)]]

This question is answered By – interjay

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