Fill a list with unique random values with F#

Question

I'm trying to learn F# but I'm stuck with a very simple thing.

I would like to create a list with uniques random values that I can display on a console. Let say Random from 1 to 100 and 10 elements in the list.

I've seen here this code F# getting a list of random numbers :

let genRandomNumbers count =
    let rnd = System.Random()
    List.init count (fun _ -> rnd.Next (1, 100))

let l = genRandomNumbers 10
printfn "%A" l

But how can I make theses numbers be differents ? This is not exactly a duplicate question because I don't find a way to be sure that each number is unique ; Random.Next can generate same numbers...

Answer 1

Here's a very simple solution:

let genRandomNumbers count =
    let rnd = System.Random()
    let initial = Seq.initInfinite (fun _ -> rnd.Next (1, 100)) 
    initial
    |> Seq.distinct
    |> Seq.take(count)
    |> Seq.toList

Note the Seq.distinct does exactly what you want to get the unique values. Also note that you'll get an issue if you try to get a count larger than 99 because there aren't that many distinct values between 1 and 99!