ActiveState Code

Recipe 576917: Functional selection sort

This is a variant of selection sort without using for-statements. Do you like it? :-)

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selection_sort = lambda sort_list: reduce(
    lambda my_list, i: (
        lambda max_value=reduce(
            lambda a, b: b if b > a else a,
            my_list[1]
        ): [
            my_list[1].remove(max_value),
            my_list[0].append(max_value)
        ] and  my_list
    )(),
    range(len(sort_list)),
    [[], sort_list]
)[0]

test_list = [ 5, 1, 7, 0, -3, -10, 10, -6, 1, 0, 2, 4, -2, 6, 5, 8, 2]
print test_list
print selection_sort(test_list)

Comments

  1. 1. At 1:11 a.m. on 2 oct 2009, Matteo Dell'Amico said:

    This is simpler and doesn't use the imperative constructs list.remove and list.append:

    def selsort(l):
    if not l: return []
    idx, v = min(enumerate(l), key=operator.itemgetter(1))
    return [v] + selsort(l[:idx] + l[idx + 1:])

    ...or was it the challenge to have it all in a single expression?

    selsort2 = (lambda l: [] if not l else
            (lambda (idx, v): [v] + selsort(l[:idx] + l[idx + 1:]))
            (min(enumerate(l), key=lambda(i, x): x)))

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