Jared Jennings:
-- Sort the [a]'s by the [b]'s. sortByKeys :: (Ord b) => [b] -> [a] -> [a] sortByKeys keys values = map snd $ sortBy compareFst (zip keys values) where compareFst x y = compare (fst x) (fst y)
Henk-Jan van Tuyl:
You can simplify that to:
sortByKeys :: (Ord b) => [b] -> [a] -> [a] sortByKeys keys values = map snd $ sort $ zip keys values
as "sort" also handles tuples; it is not fully identical, in case there are duplicate keys:
Data.List> sort [(2, 2), (2, 1), (1, 2), (1, 1)] [(1,1),(1,2),(2,1),(2,2)]
The modified version would require an ordering for the values as well as the keys, so it actually has a different type: sortByKeys :: Ord (b,a) => [b] -> [a] -> [a] The original didn't place any restrictions on the values.