when 'choices'
      values = values.sort{|a,b|( a and b ) ? a <=> b : ( a ? -1 : 1 ) }.group_by{|val| val}.collect do |key, array|
        { name: "#{self.human_normalized_value(key)} in #{self.source.name} at #{self.human_table}", y: array.size, id: key.to_s, mapping_id: self.id }