[Haskell-cafe] Splitting a list

[Joe Fasel]

On 2004.04.22 15:02, I wrote:
> splitAll :: (Real a) => a -> [a] -> [[a]]
> splitAll = unfoldr . split
> 	   where split _ [] = Nothing
>                  split n xs = let (ys,zs) = break ((> n) . snd)
>                                                   (zip xs (scanl1 (+) xs))
>                               in Just (map fst ys, map fst zs)

a slight improvement:

splitAll :: (Real a) => a -> [a] -> [[a]]
splitAll n = unfoldr split
	     where split [] = Nothing
                   split xs = let (ys,zs) = break ((> n) . snd)
                                                  (zip xs (scanl1 (+) xs))
                              in Just (map fst ys, map fst zs)

But in fact, I think you can do better still by not holding n
constant but using a higher threshold on each split and not
projecting out the values of the second component, thus only
zipping the whole list once.

--Joe

Joseph H. Fasel, Ph.D.                  email: jhf at lanl.gov
Systems Planning and Analysis           phone: +1 505 667 7158
University of California                fax: +1 505 667 2960
Los Alamos National Laboratory          post: D-2 MS F609; Los Alamos, NM 87545