CDE

Task/Entropy/D/entropy.d

@@ -0,0 +1,15 @@
+import std.stdio, std.algorithm, std.math;
+
+double entropy(T)(T[] s)
+/*pure nothrow*/ if (__traits(compiles, sort(s))) {
+    return s
+           .sort()
+           .group
+           .map!(g => g[1] / cast(double)s.length)
+           .map!(p => -p * log2(p))
+           .reduce!q{a + b};
+}
+
+void main() {
+    "1223334444"d.dup.entropy.writeln;
+}