John,
My question is, how do I preserve the ordering of entities in my
list and still be able to assign the proper order values to each
entity? Is there an efficient way to do this? How else might I
improve my orderByPriority algorithm.
Straightforwardly, you could do it like this:
import List (sortBy)
type Priority = Int
type Order = Int
order :: [Priority] -> [(Priority, Order)]
order = unlabel . sortOnLab . assignOrder . sortOnPrio . label
where
label = zip [0 ..]
unlabel = map snd
sortOnLab = sortBy (\(l, _) (m, _) -> compare l m)
sortOnPrio = sortBy (\(_, p) (_, q) -> compare p q)
assignOrder = \xs -> zipWith (\(l, p) o -> (l, (p, o))) xs [0 ..]
For instance:
> order [5, 2, 3, 7]
[(5,2),(2,0),(3,1),(7,3)]
HTH,
Stefan
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