Split a F# sequence (Seq) into chunks

gistfile1.fs

// Author: Nathan B. Evans
// Twitter: @nbevans
// Blog: https://nbevans.wordpress.com/2014/03/13/really-simple-way-to-split-a-f-sequence-into-chunks-partitions/
// License: MIT

/// Returns a sequence that yields chunks of length n.
/// Each chunk is returned as an array.
let toChunks n (s:seq<'t>) = seq {
    let pos = ref 0
    let buffer = Array.zeroCreate<'t> n

    for x in s do
        buffer.[!pos] <- x
        if !pos = n - 1 then
            yield buffer |> Array.copy
            pos := 0
        else
            incr pos

    if !pos > 0 then
        yield Array.sub buffer 0 !pos
}

// Ridiculously imperative, but it works and is performant; won't seek the sequence more than once.
// If you're using in a forward-only manner and won't be holding references to the returned chunks
// then you can get rid of the Array.copy to gain some extra perf and reduce GC.