def quartiles
      quartiles = Array.new(5) { [] }
      @raw.each_with_object(quartiles) do |elem, acc|
        acc[quartile(elem.score)] << elem
      end
    end
def quartiles
      quartiles = Array.new(5) { [] }
      @raw.each_with_object(quartiles) do |elem, acc|
        acc[quartile(elem.score)] << elem
      end
    end
Return the list split into quartiles