I'm trying to debug a program and am running into issues. Can anybody direct me to the issue here?
The program is meant to take a list of items, and returns the list of powersets for those items.
An example:
>>> getAllSubsets([1,2])
[[1,2],[1],[2],[]]
The code:
def getAllSubsets(lst):
if not lst:
return []
withFirst = [ [lst[0]] + rest for rest in getAllSubsets(lst[1:]) ]
withoutFirst = getAllSubsets(lst[1:])
return withFirst + withoutFirst
There are better recipes, yes. But I think the problem with your code is that you should replace return [] with return [[]]. The empty set is itself a subset.
There's a powerset generator in the recipes section of the itertools documentation; you should use that.
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))
I found this solution on the internet:
def powset3(seq):
if seq:
p = powset3(seq[1:])
return p + [x + seq[:1] for x in p]
else:
return [[]]
getAllSubsetstwice; call it once and save the result.