Uniquifying a list?

[Tim Chase]

Is there an obvious/pythonic way to remove duplicates from a
list (resulting order doesn't matter, or can be sorted
postfacto)? My first-pass hack was something of the form
[color=blue][color=green][color=darkred]
>>> myList = [3,1,4,1,5,9,2,6 ,5,3,5]
>>> uniq = dict([k,None for k in myList).keys()[/color][/color][/color]

or alternatively
[color=blue][color=green][color=darkred]
>>> uniq = list(set(myList ))[/color][/color][/color]

However, it seems like there's a fair bit of overhead
here...creating a dictionary just to extract its keys, or
creating a set, just to convert it back to a list. It feels
like there's something obvious I'm missing here, but I can't
put my finger on it.

Thanks...

-tkc

[Edward Elliott]

Re: Uniquifying a list?

You could do
[color=blue][color=green][color=darkred]
>>> uniq = [x for x in set(myList)][/color][/color][/color]

but that's not really any different than what you already have.

This almost works:
[color=blue][color=green][color=darkred]
>>> uniq = [x for x in myList if x not in uniq][/color][/color][/color]

except the r-val uniq isn't updated after each iteration.

Personally I think list(set(myList )) is as optimal as you'll get.


Tim Chase wrote:[color=blue]
> Is there an obvious/pythonic way to remove duplicates from a list
> (resulting order doesn't matter, or can be sorted postfacto)? My
> first-pass hack was something of the form
>[color=green][color=darkred]
> >>> myList = [3,1,4,1,5,9,2,6 ,5,3,5]
> >>> uniq = dict([k,None for k in myList).keys()[/color][/color]
>
> or alternatively
>[color=green][color=darkred]
> >>> uniq = list(set(myList ))[/color][/color]
>
> However, it seems like there's a fair bit of overhead here...creating a
> dictionary just to extract its keys, or creating a set, just to convert
> it back to a list. It feels like there's something obvious I'm missing
> here, but I can't put my finger on it.
>
> Thanks...
>
> -tkc
>
>
>
>
>[/color]

[John Machin]

Re: Uniquifying a list?

On 19/04/2006 1:31 AM, Tim Chase wrote:[color=blue]
> Is there an obvious/pythonic way to remove duplicates from a list
> (resulting order doesn't matter, or can be sorted postfacto)?[/color]

Google is your friend:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52560

[Rene Pijlman]

Re: Uniquifying a list?

Tim Chase:[color=blue]
>Is there an obvious/pythonic way to remove duplicates from a
>list (resulting order doesn't matter,[/color]

Use a set.

http://www.python.org/doc/lib/types-set.html

--
René Pijlman

[bearophileHUGS@lycos.com]

Re: Uniquifying a list?

There is my version too:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/438599

Bye,
bearophile