I can't answer your question (about getting minBy into the libraries)
but I thought I'd point out some tricks:
On Sat, Feb 20, 2010 at 10:47 AM, Andrew Coppin
Also, constructions like
sortBy (compare `on` foo)
must surely be very common.
Common enough that Data.Ord introduces comparing: comparing :: (Ord a) => (b -> a) -> b -> b -> Ordering comparing = (compare `on`) see http://hackage.haskell.org/packages/archive/base/latest/doc/html/Data-Ord.ht... But it would still be useful to have sortOn et al to capture the common technique when your sorting property is potentially expensive (sortOn length, for example): sortOn f = map fst . sortBy (comparing snd) . map (\x -> (x, f x)) a technique which I believe is called a Schwarzian transform.
Finally, take a look at this:
newtype SwapOrd x = SwapOrd (unswap_ord :: x) deriving Eq
instance Ord x => Ord (SwapOrd x) where compare x y = swap_ord $ compare x y
swap_ord :: Ordering -> Ordering swap_ord o = case o of EQ -> EQ GT -> LT LT -> GT
Just in case you wanted to sort things in reverse order. I think having swap_ord would be nice if nothing else...
swap_ord (compare x y) = compare y x, so usually flip compare fills this requirement :)