To get a historgram

histogram.ml

let most_frequent_elt list =
  let rec loop maxelt maxcount elt count = function
    | [] -> if count > maxcount then elt else maxelt
    | x::xs ->
        if elt = x then loop maxelt maxcount elt (count + 1) xs
        else if count > maxcount then loop elt count x 1 xs
        else loop maxelt maxcount x 1 xs in
  match List.sort compare list with
  | [] -> None
  | x::xs -> Some (loop x 0 x 1 xs);;

let pfactorsM (n:int) : (int * int) list =
  let incrementCounter counters prime = match (List.exists (function
    | x, y when x = prime -> true
    | _ -> false
  ) counters) with
  | true -> List.map (function
    | x, y when x = prime -> (x, y+1)
    | x, y -> (x, y)
  ) counters
    | false -> (prime, 1)::counters
  in List.rev (List.fold_left incrementCounter [] (pfactors n))
;;