haskell - Removing duplicate elements in a Seq -


wondering how implement nub on seq a

i 1 do:

nubseq :: seq -> seq nubseq = fromlist . nub . tolist

just wondering there standard not convert lists in order call nub :: [a]->[a]?

an implementation occurred me, based on nub, is:

nubseq :: (eq a) => seq -> seq nubseq = data.sequence.foldrwithindex             (\_ x -> case x `data.sequence.elemindexr` of                         _ ->                         nothing -> |> x) data.sequence.empty

but there must more elegant?

thanks.

not sure whether qualifies more elegant splits concerns in independent functions (caveat: need ord constraint on a):

  • seqtonubmap takes seq , outputs map associating each a smallest index @ appeared in sequence

  • maptolist takes map of values , positions , produces list of values in increasing order according specified positions

  • nubseq combines these generate sequence without duplicates

the whole thing should o(n*log(n)), believe:

module nubseq  import data.map      map import data.list     list import data.sequence seq import data.function  seqtonubmap :: ord => seq -> map int seqtonubmap = foldlwithindex (\ m k v -> insertwith min v k m) map.empty  maptolist :: ord => map int -> [a] maptolist = fmap fst . list.sortby (compare `on` snd) . map.tolist  nubseq :: ord => seq -> seq nubseq = seq.fromlist . maptolist . seqtonubmap

or simpler alternative following @davidfletcher's comment:

nubseq' :: forall a. ord => seq -> seq nubseq' xs = fold.foldr cons nil xs set.empty    cons :: -> (set -> seq a) -> (set -> seq a)   cons x xs seen     | x `elem` seen = xs seen     | otherwise     = x <| xs (set.insert x seen)    nil :: set -> seq   nil _ = seq.empty

Comments

Post a Comment

Popular posts from this blog

Is there a better way to structure post methods in Class Based Views -

i'm using class based views in django , never specify url in ajax calls , omit action parameter in form because know these requests go through post method of class based view. notice view - profile page make many requests depending on user updating on page - post method become convoluted , if/else mess example: def post(self, request, *args, **kwargs): # handle user changing available date if request.post.get('availabledate') != none: self.updateavailabledate(request) return jsonresponse({'result':'success'}) if request.post.get('newprojectname') != none: creative_user = creativeuserprofile.objects.get(id = request.user.id) project = project.create_project(creative_user, request.post['newprojectname']) project.save() return jsonresponse({'projectid': project.id }) if request.post.get('projectimage') != none , request.files['file']: proj...
Read more

What is happening when Matlab is starting a "parallel pool"? -

running parallel cpu processes in matlab starts command parpool() according documentation , function: [creates] special job on pool of workers, , [connects] matlab client parallel pool. this function takes bit of time execute, on order of 30 seconds. in other multi-cpu paradigms openmp, parallel execution seems totally transparent -- i've never noticed behavior analogous matlab (granted i'm not experienced parallel programming). so, happening between time parpool() called , when finishes executing? takes long? parallel computing toolbox enables run matlab code in parallel using several different paradigms (e.g. jobs , tasks, parfor , spmd , parfeval , batch processing), , run either locally (parallelised across cores in local machine) or remotely (parallelised across machines in cluster - either 1 own, or 1 in cloud). in of these cases, code run on matlab workers , copies of matlab without interactive desktop. if you're intending run on remo...
Read more

php - Cannot override Laravel Spark authentication with own implementation -

during login process of laravel spark need request token of remote api. api stores exact same users , passwords laravel spark application. therefore need username , non hashed password of user during authentication process. i thought overriding authenticated method solution problem. in routes/web.php override post /login endpoint , pointing endpoint own logincontroller: <?php namespace app\http\controllers\auth; use illuminate\support\facades\log; use illuminate\http\request; use laravel\spark\http\controllers\auth\logincontroller sparklogincontroller; class logincontroller extends sparklogincontroller { /** * create new login controller instance. * * @return void */ public function __construct() { parent::__construct(); } /** * handle successful authentication attempt. * * @param request $request * @param \illuminate\contracts\auth\authenticatable $user * @return response */ public fu...
Read more