Getting the subsets of a set in Python
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Solution 1
Look at the powerset() recipe in the itertools docs.
from itertools import chain, combinations
def powerset(iterable):
"powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)"
s = list(iterable)
return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))
def subsets(s):
return map(set, powerset(s))
Solution 2
>>> s=set(range(10))
>>> L=list(s)
>>> subs = [{L[j] for j in range(len(L)) if 1<<j&i} for i in range(1,1<<len(L))]
>>> s in subs
True
>>> set() in subs
False
Author by
geraldgreen
Updated on July 05, 2022Comments
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geraldgreen almost 2 years
Suppose we need to write a function that gives the list of all the subsets of a set. The function and the doctest is given below. And we need to complete the whole definition of the function
def subsets(s): """Return a list of the subsets of s. >>> subsets({True, False}) [{False, True}, {False}, {True}, set()] >>> counts = {x for x in range(10)} # A set comprehension >>> subs = subsets(counts) >>> len(subs) 1024 >>> counts in subs True >>> len(counts) 10 """ assert type(s) == set, str(s) + ' is not a set.' if not s: return [set()] element = s.pop() rest = subsets(s) s.add(element)
It has to not use any built-in function
My approach is to add "element" into rest and return them all, but I am not really familiar how to use set, list in Python.