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Remove duplicate list elements

I have been working on my "Functional Style" and like to think that I have improved a bit. The list order is no longer maintained in this snippet; however as the order change is simply a feature of the foldBack process the reversal of input and reversal of output is a reliable (and efficient?) fix.

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let removeDuplicates(m_list : 'a list) : 'a list =
    let reversedList = m_list |> List.rev // filter elements in original order
    let rec filterOutDuplicate i acc = 
        if i < 0 then 
                    acc |> List.rev // result returned in original order
                 else
            if List.exists(fun y -> reversedList.[i] = y) acc then
                    filterOutDuplicate (i - 1) (acc)
                else // function starts at last element of list
                    filterOutDuplicate (i - 1) (reversedList.[i] :: acc)
    filterOutDuplicate (m_list.Length - 1) List.empty

let testlist = ["e"; "j"; "f"; "h"; "d"; "i"; "k"; "l"; "g"; "a"; "b"; "c"; "d"; "e"; "f"; "g" ]
let removeDupL9 = removeDuplicates(testlist)

val removeDuplicates : m_list:'a list -> 'a list (requires equality)

Full name: Script.removeDuplicates

val m_list : 'a list (requires equality)

type 'T list = List<'T>

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

val reversedList : 'a list (requires equality)

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 filterOutDuplicate : (int -> 'a list -> 'a list) (requires equality)

val i : int

val acc : 'a list (requires equality)

val exists : predicate:('T -> bool) -> list:'T list -> bool

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

val y : 'a (requires equality)

property List.Length: int

val empty<'T> : 'T list

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

val testlist : string list

Full name: Script.testlist

val removeDupL9 : string list

Full name: Script.removeDupL9

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More information

Link:	http://fssnip.net/b3
Posted:	12 years ago
Author:	visProcessEngg
Tags:	remove duplicates , list , tail recursion