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intersperse last

Fold a string with one delimiter except for the last with a different delim. So basically if you have a list ["1";"2";"3"] and you want it to be ["1";",";"2";"and";"3]

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open System

let intersperseLast lastDelim delim list =  
    let length = Seq.length list
    Seq.scan (fun acc elem ->
                match acc with 
                | (count, state) when count < length - 1 -> (count + 1, delim::elem::state)
                | (count, state) when count = length -> (count + 1, elem::state)
                | (count, state) -> (count + 1, lastDelim::elem::state)) (1, []) list
        |> Seq.last
        |> snd        
        |> Seq.toList
        |> List.rev



let intersperseLastList lastDelim delim list = 
    let length = List.length list
    List.foldBack(fun elem acc ->
        match acc with 
                | (count, state) when count = 1 -> (count - 1, elem::state)
                | (count, state) when count = length -> (count - 1, lastDelim::elem::state)
                | (count, state) -> (count - 1, delim::elem::state)) list (length, [])

namespace System

val intersperseLast : lastDelim:'a -> delim:'a -> list:seq<'a> -> 'a list

Full name: Script.intersperseLast

val lastDelim : 'a

val delim : 'a

Multiple items
val list : seq<'a>

--------------------
type 'T list = List<'T>

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

val length : int

module Seq

from Microsoft.FSharp.Collections

val length : source:seq<'T> -> int

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

val scan : folder:('State -> 'T -> 'State) -> state:'State -> source:seq<'T> -> seq<'State>

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

val acc : int * 'a list

val elem : 'a

val count : int

val state : 'a list

val last : source:seq<'T> -> 'T

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

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

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

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

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

Multiple items
module List

from Microsoft.FSharp.Collections

--------------------
type List<'T> =
  | ( [] )
  | ( :: ) of Head: 'T * Tail: 'T list
  interface IEnumerable
  interface IEnumerable<'T>
  member Head : 'T
  member IsEmpty : bool
  member Item : index:int -> 'T with get
  member Length : int
  member Tail : 'T list
  static member Cons : head:'T * tail:'T list -> 'T list
  static member Empty : 'T list

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

val rev : list:'T list -> 'T list

Full name: Microsoft.FSharp.Collections.List.rev

val intersperseLastList : lastDelim:'a -> delim:'a -> list:'a list -> int * 'a list

Full name: Script.intersperseLastList

Multiple items
val list : 'a list

--------------------
type 'T list = List<'T>

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

val length : list:'T list -> int

Full name: Microsoft.FSharp.Collections.List.length

val foldBack : folder:('T -> 'State -> 'State) -> list:'T list -> state:'State -> 'State

Full name: Microsoft.FSharp.Collections.List.foldBack

Raw view Test code New version

More information

Link:	http://fssnip.net/kb
Posted:	10 years ago
Author:	devshorts
Tags:	list , string