Is this a good way to get all sublists of a sequence/list that have a given length?
An inefficient way to do it would be something like
f n = (filter (\x -> (length x) > n)) . (take n) . tails
This just takes the
n first elements of each tail of the original list. I think it should be slow because of the length check on every tail-element.
A smarter way would should be to "slide" a sequence of length
n over an input sequence and save the result of each slide by one to the right.
-- | Get all the subsequences of a given sequence sq of length n ngrams::Int -> Seq a -> Seq (Seq a) ngrams n sq | length sq < n = empty ngrams n sq | otherwise = ngrams' restSequence initialWindow empty where initialWindow = take n sq restSequence = drop n sq ngrams' (viewl -> EmptyL) window acc = acc |> window ngrams' (viewl -> x :< s) window@(viewl -> a :< r) acc = ngrams' s (r |> x) (acc |> window)
Somehow I have the feeling I am missing an obvious way to do this better...