Python program to get all subsets of a given size of a set

In this article, we will learn how to generate all subsets of a specific size from a given set. This is a common problem in combinatorics where we need to find all possible combinations of n elements from a larger set.

Problem statement ? We are given a set, we need to list all the subsets of size n.

We have three approaches to solve the problem using Python's itertools module ?

Using itertools.combinations() Method

The most straightforward approach uses itertools.combinations() which returns tuples of the specified size ?

import itertools

def findsubsets(s, n):
    return list(itertools.combinations(s, n))

# Driver Code
s = {1, 2, 3, 4, 5}
n = 4
print(findsubsets(s, n))

[(1, 2, 3, 4), (1, 2, 3, 5), (1, 2, 4, 5), (1, 3, 4, 5), (2, 3, 4, 5)]

Using map() with combinations() Method

This approach uses map() to convert each tuple combination back to a set format ?

import itertools
from itertools import combinations

def findsubsets(s, n):
    return list(map(set, itertools.combinations(s, n)))

# Driver Code
s = {1, 2, 3, 4, 5}
n = 4
print(findsubsets(s, n))

[{1, 2, 3, 4}, {1, 2, 3, 5}, {1, 2, 4, 5}, {1, 3, 4, 5}, {2, 3, 4, 5}]

Using List Comprehension

This method uses list comprehension to convert combinations into sets, providing a more Pythonic approach ?

import itertools

def findsubsets(s, n):
    return [set(i) for i in itertools.combinations(s, n)]

# Driver Code
s = {1, 2, 3, 4, 5}
n = 4
print(findsubsets(s, n))

[{1, 2, 3, 4}, {1, 2, 3, 5}, {1, 2, 4, 5}, {1, 3, 4, 5}, {2, 3, 4, 5}]

Comparison

Conclusion

All three methods efficiently generate subsets of a given size using itertools.combinations(). Choose tuples for ordered results or sets when order doesn't matter. List comprehension offers the most readable solution.