Just another update

Task/Entropy/JavaScript/entropy.js

@@ -0,0 +1,31 @@
+(function(shannon) {
+  // Create a dictionary of character frequencies and iterate over it.
+  function process(s, evaluator) {
+    var h = Object.create(null), k;
+    s.split('').forEach(function(c) {
+      h[c] && h[c]++ || (h[c] = 1); });
+    if (evaluator) for (k in h) evaluator(k, h[k]);
+    return h;
+  };
+  // Measure the entropy of a string in bits per symbol.
+  shannon.entropy = function(s) {
+    var sum = 0,len = s.length;
+    process(s, function(k, f) {
+      var p = f/len;
+      sum -= p * Math.log(p) / Math.log(2);
+    });
+    return sum;
+  };
+})(window.shannon = window.shannon || {});
+
+// Log the Shannon entropy of a string.
+function logEntropy(s) {
+  console.log('Entropy of "' + s + '" in bits per symbol:', shannon.entropy(s));
+}
+
+logEntropy('1223334444');
+logEntropy('0');
+logEntropy('01');
+logEntropy('0123');
+logEntropy('01234567');
+logEntropy('0123456789abcdef');