finding items that occur more than once in a list

[Arnaud Delobelle]

On Mar 18, 9:56 pm, sturlamolden <sturlamol... at yahoo.no> wrote:
> On 18 Mar, 22:25, sturlamolden <sturlamol... at yahoo.no> wrote:
>
> > def nonunique(lst):
> >    slst = sorted(lst)
> >    return list(set([s[0] for s in
> >        filter(lambda t : t[0] != t[1], zip(slst[:-1],slst[1:]))]))
>
> Obviously that should be 'lambda t : t[0] == t[1]'. Instead of using
> the set function, there is more structure to exploit when the list is
> sorted:
>
> def nonunique(lst):
>    slst = sorted(lst)
>    dups = [s[0] for s in
>         filter(lambda t : t[0] == t[1], zip(slst[:-1],slst[1:]))]
>    return [dups[0]] + [s[1] for s in
>         filter(lambda t : t[0] != t[1], zip(dups[:-1],dups[1:]))]

Argh!  What's wrong with something like:

def duplicates(l):
    i = j = object()
    for k in sorted(l):
        if i != j == k: yield k
        i, j = j, k

>>> list(duplicates([1, 2, 3, 2, 2, 4, 1]))
[1, 2]

--
Arnaud