On 21 May 2013 14:31, Treder, Robert <robert.tre...@morganstanley.com> wrote:
> Steven wrote:
>>
>> py> L = ['b', 'd', 'c', 'a', 'b']
>> py> list(set(L))
>> ['a', 'c', 'b', 'd']
>>
>>
>> If keeping the order is important, you cannot use set, and you'll need
>> another way to extract only the unique values. Ask if you need help on
>> that.
>
> Thanks, Steven. Very helpful. It looks like the order is only changed on the
> inner list that
> set() is applied to, not on the outer list since the outer list order is
> controlled by index.
> For this application I don't care about the order of the inner lists. However
> there are other
> applications where that will be import. Can you please describe the alternate
> method for
> extracting the unique values that maintains order.
There isn't necessarily a uniquely defined ordering. Here's a function
that preserves the order of the first occurrences of each element in
each list:
def uniquify(original):
new = []
seen = set()
for item in original:
if item not in seen:
new.append(item)
seen.add(item)
return new
>>> uniquify([1, 2, 3, 1, 2, 5])
[1, 2, 3, 5]
Oscar
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
