Initial data commit

Task/Entropy/JavaScript/entropy-1.js

@@ -0,0 +1,19 @@
+// Shannon entropy in bits per symbol.
+function entropy(str) {
+  const len = str.length
+
+  // Build a frequency map from the string.
+  const frequencies = Array.from(str)
+    .reduce((freq, c) => (freq[c] = (freq[c] || 0) + 1) && freq, {})
+
+  // Sum the frequency of each character.
+  return Object.values(frequencies)
+    .reduce((sum, f) => sum - f/len * Math.log2(f/len), 0)
+}
+
+console.log(entropy('1223334444'))        // 1.8464393446710154
+console.log(entropy('0'))                 // 0
+console.log(entropy('01'))                // 1
+console.log(entropy('0123'))              // 2
+console.log(entropy('01234567'))          // 3
+console.log(entropy('0123456789abcdef'))  // 4

Task/Entropy/JavaScript/entropy-2.js

@@ -0,0 +1,15 @@
+const entropy = (s) => {
+  const split = s.split('');
+  const counter = {};
+  split.forEach(ch => {
+    if (!counter[ch]) counter[ch] = 1;
+    else counter[ch]++;
+  });
+
+
+  const lengthf = s.length * 1.0;
+  const counts = Object.values(counter);
+  return -1 * counts
+    .map(count => count / lengthf * Math.log2(count / lengthf))
+    .reduce((a, b) => a + b);
+};