def init_string(data, options)
      @type, @data = File.exist?(data) ? [:datafile, "'#{data}'"] : [:math_function, data.clone]
      @options = Hamster.hash(options)
    end
def init_string(data, options)
      @type, @data = File.exist?(data) ? [:datafile, "'#{data}'"] : [:math_function, data.clone]
      @options = Hamster.hash(options)
    end
Initialize Dataset from given String