March 2014 update

Task/Entropy/AutoHotkey/entropy.ahk

@@ -0,0 +1,18 @@
+MsgBox, % Entropy(1223334444)
+
+Entropy(n)
+{
+    a := [], len := StrLen(n), m := n
+    while StrLen(m)
+    {
+        s := SubStr(m, 1, 1)
+        m := RegExReplace(m, s, "", c)
+        a[s] := c
+    }
+    for key, val in a
+    {
+        m := Log(p := val / len)
+        e -= p * m / Log(2)
+    }
+    return, e
+}

Task/Entropy/CoffeeScript/entropy.coffee

@@ -0,0 +1,13 @@
+entropy = (s) ->
+    freq = (s) ->
+        result = {}
+        for ch in s.split ""
+            result[ch] ?= 0
+            result[ch]++
+        return result
+
+    frq = freq s
+    n = s.length
+    ((frq[f]/n for f of frq).reduce ((e, p) -> e - p * Math.log(p)), 0) * Math.LOG2E
+
+console.log "The entropy of the string '1223334444' is #{entropy '1223334444'}"

Task/Entropy/D/entropy.d

@@ -1,13 +1,13 @@
 import std.stdio, std.algorithm, std.math;
 
 double entropy(T)(T[] s)
-/*pure nothrow*/ if (__traits(compiles, sort(s))) {
+/*pure nothrow*/ if (__traits(compiles, s.sort())) {
     return s
            .sort()
            .group
-           .map!(g => g[1] / cast(double)s.length)
-           .map!(p => -p * log2(p))
-           .reduce!q{a + b};
+           .map!(g => g[1] / double(s.length))
+           .map!(p => -p * p.log2)
+           .sum;
 }
 
 void main() {

Task/Entropy/Rust/entropy.rust

@@ -0,0 +1,16 @@
+// works for Rust 0.9
+fn entropy(s: &str) -> f32 {
+	let mut entropy: f32 = 0.0;
+	let mut histogram = [0, ..256];
+	let len = s.len();
+
+	for i in range(0, len) { histogram[s[i]] += 1; }
+	for i in range(0, 256) {
+		if histogram[i] > 0 {
+			let ratio = (histogram[i] as f32 / len as f32) as f32;
+			entropy -= (ratio * log2(ratio)) as f32;
+		}
+	}
+
+	entropy
+}