def column(label)
      pos = @labels.index(label)
      raise "There is no column named " + label if pos.nil?
      Mikon::Series.new(label, @data[pos], index: @index)
    end
def column(label)
      pos = @labels.index(label)
      raise "There is no column named " + label if pos.nil?
      Mikon::Series.new(label, @data[pos], index: @index)
    end
Access column with its name