Time for an 2014 update…

Task/Entropy/Seed7/entropy.seed7

@@ -0,0 +1,29 @@
+$ include "seed7_05.s7i";
+  include "float.s7i";
+  include "math.s7i";
+
+const func float: entropy (in string: stri) is func
+  result
+    var float: entropy is 0.0;
+  local
+    var hash [char] integer: count is (hash [char] integer).value;
+    var char: ch is ' ';
+    var float: p is 0.0;
+  begin
+    for ch range stri do
+      if ch in count then
+        incr(count[ch]);
+      else
+        count @:= [ch] 1;
+      end if;
+    end for;
+    for key ch range count do
+      p := flt(count[ch]) / flt(length(stri));
+      entropy -:= p * log(p) / log(2.0);
+    end for;
+  end func ;
+
+const proc: main is func
+  begin
+    writeln(entropy("1223334444") digits 5);
+  end func;