lib/earth/pet/species.rb in earth-0.3.13 vs lib/earth/pet/species.rb in earth-0.3.14

@@ -2,20 +2,29 @@
   set_primary_key :name
   
   scope :thoroughly_researched, :conditions => 'marginal_dietary_requirement IS NOT NULL'
   
   falls_back_on :diet_emission_intensity => lambda { weighted_average :diet_emission_intensity, :weighted_by => :population }, # kg CO2 / joule
-                :marginal_dietary_requirement => lambda { (thoroughly_researched.map(&:weighted_diet_size).sum / thoroughly_researched.sum(:population) ) / thoroughly_researched.weighted_average(:weight, :weighted_by => :population)}, # joules
+                :marginal_dietary_requirement => lambda { Species.marginal_dietary_requirement_fallback },
                 :fixed_dietary_requirement => 0, # force a zero intercept to be respectful of our tiny tiny animal friends
                 :weight => lambda { weighted_average :weight, :weighted_by => :population } # kg
 
   data_miner do
     tap "Brighter Planet's species data", Earth.taps_server
   end
   
   class << self
     def [](name)
       find_by_name name.to_s
+    end
+
+    def marginal_dietary_requirement_fallback
+      total_diet_size = thoroughly_researched.map(&:weighted_diet_size).sum
+      total_population = thoroughly_researched.sum(:population)
+      return 0.0 unless total_population > 0.0
+      average_weight = thoroughly_researched.weighted_average(:weight, :weighted_by => :population)
+      return 0.0 unless average_weight > 0.0
+      (total_diet_size / total_population) / average_weight
     end
   end
   
   def diet_size
     return unless weight and marginal_dietary_requirement and fixed_dietary_requirement