arrays - F# array_chunk for Sequence

Question

I'm having some trouble making a sequence. Basically I need to chop a sequence into a sequence of arrays. Seq.windowed almost does it but I don't want duplicate elements.

I can get what I want by reading everything into an array first but I'd rather use a sequence.

let array_chunk s (a:int[]) =
    Array.init (a.Length / s) (fun i -> Array.sub a (i * s) s)

someSequence |> Seq.to_array |> array_chunk 5

Answer 1

This answer will probably get buried, but here's my take on the problem:

let chunk n xs = 
    xs 
    |> Seq.mapi(fun i x -> i/n, x)
    |> Seq.groupBy fst
    |> Seq.map (fun (_, g) -> Seq.map snd g)

Pros:

• Uses only seq, no arrays
• O(n) runtime. Not O(n^2) like Seq.skip/take solutions
• Seq.length doesn't have to be a multiple of n
• small and easy to understand?

Cons:

• probably not as efficient as imperative/mutable loops