properly convert this into CSV string

        x_opt = self.current_axis_options[x_type]

        if x_opt.choices is not None and not csv_mode:

            x_values = ",".join(x_values_dropdown)

            x_values = list_to_csv_string(x_values_dropdown)

        xs = process_axis(x_opt, x_values, x_values_dropdown)

        y_opt = self.current_axis_options[y_type]

        if y_opt.choices is not None and not csv_mode:

            y_values = ",".join(y_values_dropdown)

            y_values = list_to_csv_string(y_values_dropdown)

        ys = process_axis(y_opt, y_values, y_values_dropdown)

        z_opt = self.current_axis_options[z_type]

        if z_opt.choices is not None and not csv_mode:

            z_values = ",".join(z_values_dropdown)

            z_values = list_to_csv_string(z_values_dropdown)

        zs = process_axis(z_opt, z_values, z_values_dropdown)

        # this could be moved to common code, but unlikely to be ever triggered anywhere else