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Break sequence into n-element subsequences

I'm working on parallel computations and I thought it would be useful to break work into chunks, especially when processing each element asynchronously is too expensive. The neat thing is that this function is general even though motivation for it is specific. Another neat thing is that this is true lazy sequence unlike what you'd get if you used Seq.groupBy. There are three versions for your enjoyment.

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let tuple2 x y = x, y
module Seq=
    let trim n = Seq.map snd << Seq.filter (fst >> (<=) n) << Seq.mapi tuple2
    let breakBy n s = 
        let rec loop s = 
            seq { if not (Seq.isEmpty s) then 
                    yield (s |> Seq.truncate n)
                    yield! loop (s |> trim n) }
        loop s

seq {1..25000} |> Seq.breakBy 50
(*
val it : seq<seq<int>> =
  seq
    [seq [1; 2; 3; 4; ...]; seq [51; 52; 53; 54; ...];
     seq [101; 102; 103; 104; ...]; seq [151; 152; 153; 154; ...]; ...]
*)

val tuple2 : x:'a -> y:'b -> 'a * 'b

Full name: Script.tuple2

val x : 'a

val y : 'b

module Seq

from Microsoft.FSharp.Collections

val trim : n:int -> (seq<'a> -> seq<'a>)

Full name: Script.Seq.trim

val n : int

val map : mapping:('T -> 'U) -> source:seq<'T> -> seq<'U>

Full name: Microsoft.FSharp.Collections.Seq.map

val snd : tuple:('T1 * 'T2) -> 'T2

Full name: Microsoft.FSharp.Core.Operators.snd

val filter : predicate:('T -> bool) -> source:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.filter

val fst : tuple:('T1 * 'T2) -> 'T1

Full name: Microsoft.FSharp.Core.Operators.fst

val mapi : mapping:(int -> 'T -> 'U) -> source:seq<'T> -> seq<'U>

Full name: Microsoft.FSharp.Collections.Seq.mapi

val breakBy : n:int -> s:seq<'a> -> seq<seq<'a>>

Full name: Script.Seq.breakBy

val s : seq<'a>

val loop : (seq<'b> -> seq<seq<'b>>)

val s : seq<'b>

Multiple items
val seq : sequence:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Core.Operators.seq

--------------------
type seq<'T> = System.Collections.Generic.IEnumerable<'T>

Full name: Microsoft.FSharp.Collections.seq<_>

val not : value:bool -> bool

Full name: Microsoft.FSharp.Core.Operators.not

val isEmpty : source:seq<'T> -> bool

Full name: Microsoft.FSharp.Collections.Seq.isEmpty

val truncate : count:int -> source:seq<'T> -> seq<'T>

Full name: Microsoft.FSharp.Collections.Seq.truncate

Multiple items
module Seq

from Script

--------------------
module Seq

from Microsoft.FSharp.Collections

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More information

Link:	http://fssnip.net/1o
Posted:	14 years ago
Author:	Dmitri Pavlenkov
Tags:	seq