CODEWITHSUNDEEP
pythonsetsubset
Randomblue
Randomblue

Reputation: 116273

Set of all subsets

In Python2 I could use

def subsets(mySet):
    return reduce(lambda z, x: z + [y + [x] for y in z], mySet, [[]])

to find all subsets of mySet. Python 3 has removed reduce.

What would be an equally concise rewrite of this for Python3?

Upvotes: 14

Views: 15329

Answers (2)

Óscar López
Óscar López

Reputation: 236004

Here's a list of several possible implementations of the power set (the set of all subsets) algorithm in Python. Some are recursive, some are iterative, some of them don't use reduce. Plenty of options to choose from!

Upvotes: 15

Sven Marnach
Sven Marnach

Reputation: 601529

The function reduce() can always be reaplaced by a for loop. Here's a Python implementation of reduce():

def reduce(function, iterable, start=None):
    iterator = iter(iterable)
    if start is None:
        start = next(iterator)
    for x in iterator:
        start = function(start, x)
    return start

(In contrast to Python's built-in version of reduce(), this version does not allow to pass in None as start parameter.)

Special-casing this code with the parameters you passed to reduce() gives

def subsets(my_set):
    result = [[]]
    for x in my_set:
        result = result + [y + [x] for y in result]
    return result

Upvotes: 5

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