Suppose you needed to shuffle the numbers 0 to 9 in F#, perhaps for a game or a data science exercise.

A simple way to do it would be as follows:

// We need this for the Random class
open System

// Generate a list of numbers
let numbers = [ 0 .. 9 ]

// Wite a function that shuffles a passed list and returns a new one
let shuffle list =
    list |> List.sortBy (fun _ -> Random.Shared.Next())

// Shuffle the numbers
let shuffledNumbers = shuffle numbers
printfn "Shuffled: %A" shuffledNumbers

If you run this code a couple of times, you should see the following

Shuffled: [3; 1; 0; 9; 2; 8; 6; 7; 4; 5]
Shuffled: [4; 5; 1; 7; 6; 0; 2; 3; 8; 9]
Shuffled: [0; 1; 2; 3; 4; 6; 5; 7; 9; 8]
Shuffled: [0; 1; 3; 2; 7; 4; 5; 6; 9; 8]
Shuffled: [1; 0; 2; 3; 5; 4; 7; 6; 8; 9]

There have been some improvements in F# that improves this.

Support for shuffling has directly been added to the various collections - List, Seq and Array

You can now rewrite the code like this:

let otherShuffledNumbers = numbers |> List.randomShuffle
printfn "Other Shuffled: %A" shuffledNumbers

To enjoy this goodness, you need to install the FSharp.Core nuget package to your program

Arrays have the additional bonus that the original array can be mutated and shuffled in place

// Create the array
let numbersArray = [0 .. 9] |> List.toArray
printfn "Original Array: %A" numbersArray

// Shuffle in place
numbersArray |> Array.randomShuffleInPlace
printfn "Original Array: %A" numbersArray

This prints the following:

Original Array: [|0; 1; 2; 3; 4; 5; 6; 7; 8; 9|]
Original Array: [|5; 9; 3; 4; 1; 6; 0; 7; 2; 8|]

The code is in my Github.

Happy hacking!