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| − | [[Category:Proposals]] | + | see [[List function suggestions]]. |
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| − | I was a bit annoyed when I found out that Data.List.groupBy compared each new element to the first element of a group instead of the last added element.
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| − | I guess the current way it is easier to implement, but severely hinders its usefulness:
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| − | <haskell>
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| − | > groupBy (\a b -> a+1 == b) [1,2,3,4,6]
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| − | [[1,2],[3,4],[6]]
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| − | </haskell>
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| − | I propose a different implementation of groupBy which would result in the following:
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| − | <haskell>
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| − | > groupBy (\a b -> a+1 == b) [1,2,3,4,6]
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| − | [[1,2,3,4],[6]]
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| − | </haskell>
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| − | The following a naive implementation that was written for "workiness" instead of speed or space behavior:
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| − | <haskell>
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| − | groupBy' :: (a -> a -> Bool) -> [a] -> [[a]]
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| − | groupBy' _ [] = []
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| − | groupBy' f (x:xs) = gb f xs [[x]]
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| − | where gb f (x:xs) ((a:as):bs) = gb f xs $ if f a x then ((x:a:as):bs)
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| − | else ([x]:(a:as):bs)
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| − | gb _ [] as = reverse . map reverse $ as
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| − | </haskell>
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| − | I'm sure there are much nicer ways to implement this...
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Latest revision as of 09:57, 6 September 2007