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

Difficulty Level : Easy
Last Updated : 05 Feb, 2019

Given a set, write a Python program to generate all possible subset of size n of given set within a list.

Examples:

Input : {1, 2, 3}, n = 2
Output : [{1, 2}, {1, 3}, {2, 3}]

Input : {1, 2, 3, 4}, n = 3
Output : [{1, 2, 3}, {1, 2, 4}, {1, 3, 4}, {2, 3, 4}]

We have already discussed the same problem using Naive approach in this article. This article focuses on the Pythonic approaches to Print all subsets of given size of a set.

Python has itertools.combinations(iterable, n) which Return n length subsequences of elements from the input iterable. This can be used to Print all subsets of given size of a set. Now, we have various alternatives to use this function.

Code #1 :
Simply pass the set as iterable and the size as arguments in the itertools.combinations() to directly fetch the combination list.

# Python Program to Print 
# all subsets of given size of a set
  
import itertools
  
def findsubsets(s, n):
    return list(itertools.combinations(s, n))
  
# Driver Code
s = {1, 2, 3}
n = 2
  
print(findsubsets(s, n))

Output:

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

Code #2 :
We can also use an alternative to above discussed method which is mapping set to itertools.combinations() function.

# Python Program to Print 
# all subsets of given size of a set
  
import itertools
from itertools import combinations, chain
  
def findsubsets(s, n):
    return list(map(set, itertools.combinations(s, n)))
      
# Driver Code
s = {1, 2, 3}
n = 2
  
print(findsubsets(s, n))

Output:

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

Code #3 :
Another method is to use for loop in itertools.combinations() function and append the combination sets to the list.

# Python Program to Print 
# all subsets of given size of a set
  
import itertools
# def findsubsets(s, n):
def findsubsets(s, n):
    return [set(i) for i in itertools.combinations(s, n)]
      
# Driver Code
s = {1, 2, 3, 4}
n = 3
  
print(findsubsets(s, n))

Output:

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

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