Weighted random selection using Walker's Alias Method

Question

I was looking for this algorithm
(algorithm which will randomly select from a list of elements where each element has different probability of being

Answer 1

open System

let oo = dict [ "A", 7;
                "B", 1;
                "C", 9;
                "D", 8;
                "E", 11 ]

let rnd = Random()
let pick = oo.Values |> Seq.sum |> rnd.Next

let res = oo |> Seq.scan (fun (_, s) (KeyValue(k, v)) -> k, s + v) ("", 0)
             |> Seq.tryPick (fun (k, s) -> if s >= pick 
                                           then printfn "Result is %s" k; Some k 
                                           else None)