geniusfat wrote:
hi dear haskell lover ;)
what I want to do is simply this:
select3 :: [a] -> [(a, a, a)]
and how can it be done efficiently?
thanks in advance!
If, given [1,2,3,4,5,6,7,8,9,10,11,12] you want
[(1,2,3),(4,5,6),(7,8,9)....] then:
map (take 3) . iterate (drop 3)
is very nearly what you need.
Two problems: (a) it gives you [[1,2,3],[4,5,6]..] instead
(b) it carries on with an infinite number of [] empty lists
you can fix both of these:
map (\[a,b,c]->(a,b,c)) . takeWhile (not.null) . map (take 3) . iterate
(drop 3)
Prelude> map (\[a,b,c] -> (a,b,c)) . takeWhile (not.null) . map (take 3)
. iterate (drop 3) $ [1..12]
[(1,2,3),(4,5,6),(7,8,9),(10,11,12)]
Hope that helps.
Jules
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