def values substance,feature
      substance = substance.id if substance.is_a? Substance
      feature = feature.id if feature.is_a? Feature
      if data_entries[substance.to_s] and data_entries[substance.to_s][feature.to_s]
        data_entries[substance.to_s][feature.to_s]
      else
        [nil]
      end
    end
def values substance,feature
      substance = substance.id if substance.is_a? Substance
      feature = feature.id if feature.is_a? Feature
      if data_entries[substance.to_s] and data_entries[substance.to_s][feature.to_s]
        data_entries[substance.to_s][feature.to_s]
      else
        [nil]
      end
    end
Get all values for a given substance and feature
 @param [OpenTox::Substance,BSON::ObjectId,String] substance or substance id
 @param [OpenTox::Feature,BSON::ObjectId,String] feature or feature id
 @return [TrueClass,FalseClass,Float]