f# - Array2D to Array

Question

I have Array2D of 0 and 1:

let rnd = System.Random()
let a = Array2D.init n n (fun i j  -> int(System.Math.Round(rnd.NextDouble() / index)) )

I need to calculate the count of '1'-elements, something like:

a |> Array.filter (fun x -> x == 1)

But 'a' is Array2D (not Array) so I'm just wondering if there is a standard way to transform Array2D to Array?

Answer 1

Here is one easy way, using the fact that [,] implements ienumerable<_>

a |> Seq.cast<int> |> Seq.filter (fun x -> x == 1)

but if you only need the count you can do

a |> Seq.cast<int> |> Seq.sum

as the 0 terms won't add to the sum and the terms you want to count are just 1