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

Here is the similar code in F#:

let rng = new System.Random()
let d = [| "A", 3
           "B", 2
           "C", 3 |]
let sums = Seq.scan (+) 0 (dict d).Values |> Seq.skip 1 |> Seq.toArray 
let pick = rng.Next(sums.[sums.Length-1])
let res = fst d.[sums |> Seq.findIndex ((<) pick)]

Answer 2

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)