Data commit

Task/Entropy-Narcissist/Erlang/entropy-narcissist.erl

@@ -0,0 +1,24 @@
+#! /usr/bin/escript
+
+-define(LOG2E, 1.44269504088896340735992).
+
+main(_) ->
+    Self = escript:script_name(),
+    {ok, Contents} = file:read_file(Self),
+    io:format("My entropy is ~p~n", [entropy(Contents)]).
+
+entropy(Data) ->
+    Frq = count(Data),
+    maps:fold(fun(_, C, E) ->
+                  P = C / byte_size(Data),
+                  E - P*math:log(P)
+              end, 0, Frq) * ?LOG2E.
+
+count(Data) -> count(Data, 0, #{}).
+count(Data, I, Frq) when I =:= byte_size(Data) -> Frq;
+count(Data, I, Frq) ->
+    Chr = binary:at(Data, I),
+    case Frq of
+        #{Chr := K} -> count(Data, I+1, Frq #{Chr := K+1});
+        _ -> count(Data, I+1, Frq #{Chr => 1})
+    end.