Best way to condense a list of option type down to only elements that are not none?

Question

I\'m unexpectedly having a bit of trouble with going from a list of \'a option down to a list containing only the elements that are Some.

My initial attempt was:

Answer 1

Simply

List.choose id

as in

> [Some 4; None; Some 2; None] |> List.choose id;;
val it : int list = [4; 2]

List.choose

id

Answer 2

Another way is to use the Option module functions to filter out the Options with values and then create a list of the values:

let concreteTypeList =
    optionTypeList
    |> List.filter (fun v -> Option.isSome v)
    |> List.map (fun v -> Option.get v)