finding items that occur more than once in a list

[Chris]

On Mar 18, 11:57 am, Simon Forman <sajmik... at gmail.com> wrote:
> Is there a more efficient way to do this?
>
> def f(L):
>     '''Return a set of the items that occur more than once in L.'''
>     L = list(L)
>     for item in set(L):
>         L.remove(item)
>     return set(L)
>
> |>> f([0, 0, 1, 1, 2, 2, 3])
> set([0, 1, 2])

def f(L):
    D = dict()
    for item in L:
        if item in D:
            D[item] += 1
        else:
            D[item] = 1
    return [i for i,j in D.items() if j > 1]

That would be my way to do it, would need to test it via several
thousand iterations to see which one is most efficient though.