Best way to make a list unique?

[Diez B. Roggisch]

Eric Pederson wrote:

> I have
> 
>>>> listA=[1,2,3,4,5,4,3,4,3,2,1]
> 
> and I want a list of only the unique members.
> 
> This seems inefficient, but works fine over my small sample lists:
> 
>>>> listA=[a for a in set(listA)]
> 
> 
> Is there a more efficient approach for cases where listA is large?

No. But I doubt that that is what you actually want, as listA will lose its
order afterwards. Typically, something like that gets written like this:

inserted = set()
res = []
for e in listA:
   if not e in inserted:
       res.append(e)
       inserted.add(e)
listA = res

Or, with a little helperfunction:

inserted = set()
def foo(e):
    inserted.add(e)
    return e
listA = [foo(e) for e in listA if not e in inserted]

But ist's not really much better.

-- 
Regards,

Diez B. Roggisch