How should one implement a chunking (or partitioning) function for F# sequences? I'm looking for a function with this signature...
val toChunks : n:int -> sequence:seq<'T> -> seq<seq<'T>>
...which returns the items of the original sequence in groups of n items. The input sequence may be unending.
Simple Example
[1; 2; 3; 4; 5; 6; 7; 8; 9]
|> toChunks 4
|> Seq.iter (printfn "%A")
seq [1; 2; 3; 4]
seq [5; 6; 7; 8]
seq [9]
Nathan Evans suggested this solution:
/// Returns a sequence that yields chunks of length n.
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
}
It seems like the best approach to me, but I'd be interested in other solutions.