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Seq.groupAfter function

This snippet is basically the same as http://fssnip.net/6A, except that the element whose predicate holds ends the previous group and the element after it starts a new one. Those two snippets (Seq.groupWhen, Seq.groupAfter) would be generally equivalent to the Haskell functions 'breakBefore' and 'breakAfter' from Data.List.Grouping.

Implementation

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module Seq =
/// Iterates over the elements of the input sequence and groups adjacent
/// elements. A new group is started after the specified predicate holds 
/// about the element of the sequence (and at the beginning of the iteration).
    let groupAfter f (input:seq<_>) = 
        use en = input.GetEnumerator()
        let rec group() =
            [   yield en.Current
                if not(f en.Current) && en.MoveNext() then
                    yield! group() ]
        seq{
            while en.MoveNext() do
                yield group() |> Seq.ofList }

Example

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[3;3;2;4;1;2] |> Seq.groupAfter (fun n -> n%2 = 1);;
/// val it : seq<seq<int>> = seq [[3]; [3]; [2; 4; 1]; [2]]

module Seq

from Microsoft.FSharp.Collections

val groupAfter : f:('a -> bool) -> input:seq<'a> -> seq<seq<'a>>

Full name: Script.Seq.groupAfter

Iterates over the elements of the input sequence and groups adjacent
elements. A new group is started after the specified predicate holds
about the element of the sequence (and at the beginning of the iteration).

val f : ('a -> bool)

val input : seq<'a>

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 en : System.Collections.Generic.IEnumerator<'a>

System.Collections.Generic.IEnumerable.GetEnumerator() : System.Collections.Generic.IEnumerator<'a>

val group : (unit -> 'a list)

property System.Collections.Generic.IEnumerator.Current: 'a

val not : value:bool -> bool

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

System.Collections.IEnumerator.MoveNext() : bool

val ofList : source:'T list -> seq<'T>

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

Multiple items
module Seq

from Script

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

from Microsoft.FSharp.Collections

val n : int

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More information

Link:	http://fssnip.net/90
Posted:	12 years ago
Author:	Thorsten Meinecke
Tags:	sequences , seq , grouping , ienumerator