minimumOn function #331

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1. lehins commented on Sep 21, 2020

   

   lehins

   on Sep 21, 2020

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   @Boarders I can see how such function can be useful (especially for Storable, Unbox and Prim, when b doesn't have an instance, while a does), but there is a problem with your suggested implementation. Namely function f will be evaluated 2*n - 1 times and in case when f is really expensive this could be very noticeable.

   A possibly better solution would be to first zip with that function over:

   minimumOn :: (Ord b, Vector v a) => (a -> b) -> v a -> a
   {-# INLINE minimumOn #-}
   minimumOn f = fst . Bundle.foldl1' minBy . Bundle.map (\a -> (a, f a)) . stream
     where
       {-# INLINE minBy #-}
       minBy x y = case compare (snd x) (snd y) of
                     GT -> y
                     _  -> x

   If anyone is willing to implement this and maximumOn for all vector types with docs, tests and at least one benchmark, I would not be opposed to merging such addition.

   👍React with 👍3Reacted by Callan McGill, ˌbodʲɪˈɡrʲim and Claudi Lleyda Moltó
2. lehins

   added a commit that references this issue on Jan 17, 2021

   Merge pull request #356 from claudi/331-minimumOn-maximumOn

   ...

   a91fe1d
3. Shimuuar commented on Jan 17, 2021

   

   Shimuuar

   on Jan 17, 2021

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   Fixed by #356
4. Shimuuar

   closed this as completedon Jan 17, 2021