Just another update

Task/Entropy/OCaml/entropy.ocaml

@@ -0,0 +1,30 @@
+(* generic OCaml, using a mutable Hashtbl *)
+
+(* pre-bake & return an inner-loop function to bin & assemble a character frequency map *)
+let get_fproc (m: (char, int) Hashtbl.t) :(char -> unit)  =
+  (fun (c:char) -> try
+                     Hashtbl.replace m c ( (Hashtbl.find m c) + 1)
+                   with Not_found -> Hashtbl.add m c 1)
+
+
+(* pre-bake and return an inner-loop function to do the actual entropy calculation *)
+let get_calc (slen:int) :(float -> float) =
+  let slen_float = float_of_int slen in
+  let log_2 = log 2.0 in
+
+  (fun v -> let pt = v /. slen_float in
+                pt *. ((log pt) /. log_2) )
+
+
+(* main function, given a string argument it:
+       builds a (mutable) frequency map (initial alphabet size of 255, but it's auto-expanding),
+       extracts the relative probability values into a list,
+       folds-in the basic entropy calculation and returns the result. *)
+let shannon (s:string) :float  =
+  let freq_hash = Hashtbl.create 255 in
+  String.iter (get_fproc freq_hash) s;
+
+  let relative_probs = Hashtbl.fold (fun k v b -> (float v)::b) freq_hash [] in
+  let calc = get_calc (String.length s) in
+
+   -1.0 *. List.fold_left (fun b x -> b +. calc x) 0.0 relative_probs