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Cross Join Lists

Given a list of lists, the function crossJoin outputs all combination of elements from the inner lists, i.e. each combination is a list which contains elements from each of the inner lists in the input. Note: Order is not preserved

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let crossJoin xss = 
    let rec outerListLoop acc xs =
        match xs with
        | [] -> acc
        | x::rest -> innerListLoop acc x rest
    and innerListLoop acc ys xs =
        match ys with
        | []    -> acc
        | y::rest -> 
            let acc' = (y::List.head acc)::List.tail acc
            let os = outerListLoop acc' xs
            let is = innerListLoop acc rest xs 
            os @ if rest |> List.isEmpty then List.tail is else is
    let xss' = xss |> List.filter (fun xs -> List.length xs > 0)
    outerListLoop [[]] xss'


(*
let data = [[1;2];[3;7];[4;5;6]] 
crossJoin data
val it : int list list =
  [[4; 3; 1]; [5; 3; 1]; [6; 3; 1]; [4; 7; 1]; [5; 7; 1]; [6; 7; 1]; [4; 3; 2];
   [5; 3; 2]; [6; 3; 2]; [4; 7; 2]; [5; 7; 2]; [6; 7; 2]]
*)

val crossJoin : xss:'a list list -> 'a list list

Full name: Script.crossJoin

val xss : 'a list list

val outerListLoop : ('b list list -> 'b list list -> 'b list list)

val acc : 'b list list

val xs : 'b list list

val x : 'b list

val rest : 'b list list

val innerListLoop : ('b list list -> 'b list -> 'b list list -> 'b list list)

val ys : 'b list

val y : 'b

val rest : 'b list

val acc' : 'b list list

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 head : list:'T list -> 'T

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

val tail : list:'T list -> 'T list

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

val os : 'b list list

val is : 'b list list

val isEmpty : list:'T list -> bool

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

val xss' : 'a list list

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

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

val xs : 'a list

val length : list:'T list -> int

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

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More information

Link:	http://fssnip.net/r2
Posted:	9 years ago
Author:	Faisal Waris
Tags:	list , join