code: def prepare_c3_time_series(data: List[Tuple[int, int]], y_axis_label: str = 'y', x_axis_label: str = 'x') -> str:
      
      years, counter = zip(*data)
  
      years = [
          datetime.date(year, 1, 1).isoformat()
          for year in years
      ]
  
      return json.dumps([
          [x_axis_label] + list(years),
          [y_axis_label] + list(counter)
      ])
docs: Prepare C3 JSON string dump for a time series.
  
      :param data: A list of tuples [(year, count)]
      :param y_axis_label: The Y axis label
      :param x_axis_label: X axis internal label. Should be left as default 'x')