Code Golf: Quickly Build List of Keywords from Text, Including # of Instances

Answer 1

F#: 304 chars

let f =
    let bad = Set.of_seq ["and";"is";"the";"of";"are";"by";"it"]
    fun length occurrence msg ->
        System.Text.RegularExpressions.Regex.Split(msg, @"[^\w-']+")
        |> Seq.countBy (fun a -> a)
        |> Seq.choose (fun (a, b) -> if a.Length > length && b > occurrence && (not <| bad.Contains a) then Some a else None)