[Haskell-cafe] ordNub

[Ivan Lazar Miljenovic]

On 16 July 2013 11:46, John Lato <jwlato at gmail.com> wrote:
> In my tests, using unordered-containers was slightly slower than using Ord,
> although as the number of repeated elements grows unordered-containers
> appears to have an advantage.  I'm sure the relative costs of comparison vs
> hashing would affect this also.  But both are dramatically better than the
> current nub.
>
> Has anyone looked at Bart's patches to see how difficult it would be to
> apply them (or re-write them)?

If I understand correctly, this function is proposed to be added to
Data.List which lives in base... but the proposals here are about
using either Sets from containers or HashSet from
unordered-containers; I thought base wasn't supposed to depend on any
other package :/

>
>
>
> On Mon, Jul 15, 2013 at 8:43 PM, Clark Gaebel <cgaebel at uwaterloo.ca> wrote:
>>
>> Apologies. I was being lazy. Here's a stable version:
>>
>>   import qualified Data.HashSet as S
>>
>>   hashNub :: (Ord a) => [a] -> [a]
>>   hashNub l = go S.empty l
>>     where
>>       go _ []     = []
>>       go s (x:xs) = if x `S.member` s then go s xs
>>                                     else x : go (S.insert x s) xs
>>
>> Which, again, will probably be faster than the one using Ord, and I
>> can't think of any cases where I'd want the one using Ord instead. I
>> may just not be creative enough, though.
>>
>>
>>   - Clark
>>
>> On Mon, Jul 15, 2013 at 12:46 AM, Brandon Allbery <allbery.b at gmail.com>
>> wrote:
>> > On Sun, Jul 14, 2013 at 7:54 AM, Clark Gaebel <cgaebel at uwaterloo.ca>
>> > wrote:
>> >>
>> >> Oops sorry I guess my point wasn't clear.
>> >>
>> >> Why ord based when hashable is faster? Then there's no reason this has
>> >> to
>> >> be in base, it can just be a
>> >
>> > Did the point about "stable" fly overhead?
>> >
>> > --
>> > brandon s allbery kf8nh                               sine nomine
>> > associates
>> > allbery.b at gmail.com
>> > ballbery at sinenomine.net
>> > unix, openafs, kerberos, infrastructure, xmonad
>> > http://sinenomine.net
>>
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>
>
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-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
http://IvanMiljenovic.wordpress.com