Kurt Hutchinson wrote: > On 4/12/07, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: >> To get the indices, use the Schwartzian transform: >> >> sortWith :: (Ord b) => (a -> b) -> [a] -> [a] >> sortWith f = mergeRuns . runs >> where >> runs = map (:[]) >> >> mergeRuns [] = [] >> mergeRuns [xs] = xs >> mergeRuns xss = mergeRuns (mergeRun xss) >> >> mergeRun (xs1:xs2:xss) = mergeOne xs1 xs2 : mergeRun xss >> mergeRun xss = xss >> >> mergeOne [] ys = ys >> mergeOne xs [] = xs >> mergeOne xs'@(x:xs) ys':(y:ys) >> = case compare (f x) (f y) of >> LT -> x : mergeOne xs ys' >> GT -> y : mergeOne xs' ys >> EQ -> x : y : mergeOne xs ys >> >> getKMinima :: (Ord a) => [a] -> [Int] >> getKMinima k = map fst . take k . sortWith snd . zip [0..] > > For my own edification, what is the benefit of this sortWith over sortBy? > > f `on` g = \ x y -> f ( g x ) ( g y ) > kminima k = map fst . take k . sortBy ( compare `on` snd ) . zip [0..]
possibly related (newbie question): pairs are instances of Ord, why not directly sort those (implying the item to be sorted is fst): > kminima k = \list -> map snd $ take k $ sort $ zip list [0..]
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