Simplify with #sum

lib/core_extensions/array.rb

@@ -2,9 +2,10 @@ class Array
   def entropy
     each_with_object(Hash.new(0)) do |i, result|
       result[i] += 1
-    end.values.inject(0) do |sum, count|
+    end.values.sum do |count|
       percentage = count.to_f / length
-      sum + -percentage * Math.log2(percentage)
+
+      -percentage * Math.log2(percentage)
     end
   end
 end