app/models/punch.rb in punching_bag-0.2.0 vs app/models/punch.rb in punching_bag-0.3.0

@@ -89,9 +89,21 @@
     unless year_combo?
       combine_with find_combo_for(:year)
     end
   end
 
+  def self.average_for(punchables)
+    if punchables.map(&:class).uniq.length != 1
+      raise ArgumentError, 'Punchables must all be of the same class'
+    end
+
+    sums = Punch.where(:punchable_type => punchables.first.class.to_s, :punchable_id => punchables.map(&:id)).group(:punchable_id).sum(:hits)
+
+    return 0 if sums.empty? # catch divide by zero
+
+    sums.values.inject(:+).to_f / sums.length    
+  end
+
   private
   
   def set_defaults
     if date = (self.starts_at ||= DateTime.now)
       self.ends_at ||= date