Python program to get all unique combinations of two Lists

Last Updated : 25 Nov, 2024

The goal is to combine each item from first list with each item from second list in every possible unique way. If we want to get all possible combinations from two lists. Python’s itertools library has a function called a product that makes it easy to generate combinations of items from multiple lists.

Python

import itertools  a = ["a", "b"] b = [1, 2]  #It generate all possible combinations of elements from both lists # Convert the result into a list of tuples combinations = list(itertools.product(a, b))  print(combinations)

Output

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

itertools.product automatically creates the combinations of elements from both lists. We use list() to convert the result into a list of tuples.

There are other methods which can be used that are both fast and efficient :

Table of Content

Using itertools.permutations

itertools.permutations function creates all possible permutations of a given list. We can combine this with zip to create unique combinations of two lists.

Python

import itertools  a = ["a", "b"] b = [1, 2]  # Generate all 2-length permuations of pairs by zipping lists combinations = list(itertools.permutations(zip(a, b), 2)) print(combinations)

Output

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

The zip(a, b) combines the two lists element-wise into pairs, and itertools.permutations then creates all possible orders of these pairs.
This method returns all unique permutations, including reversed combinations.

Using a Nested Loop

We can get all combinations is by using two loops. We can loop through each element in both lists and combine them.

Python

X = ["a", "b"] Y = [1, 2]  # Initialize an empty list  combinations = []  # Loop through each element in List_1 for x in X:     # Loop through each element in List_2     for y in Y:         combinations.append((x, y))  print(combinations)

Output

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

Using List Comprehension

If we have to write cleaner and shorter code, we can use list comprehension to achieve the same result. This is essentially the same thing as using loops but in a single line. It’s a concise way to combine elements.

Python

X = ["a", "b"] Y = [1, 2]  #list combination of all possible elemenst of two lists(X and Y) combinations = [(x, y) for x in X for y in Y]  print(combinations)

Output

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

Python - Print all common elements of two lists

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Python program to get all unique combinations of two Lists

Using itertools.permutations

Using a Nested Loop

Using List Comprehension

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