Small refactor

app/services/tables/distribution.rb

@@ -60,9 +60,7 @@ module Tables
     end
 
     def number_of_groups(table)
-      table.map do |person|
-        person.affinity_groups
-      end.flatten.uniq.count
+      table.map(&:affinity_groups).flatten.uniq.count
     end
   end
 end