code: def vectorized_sunday_to_monday(dtix):
      
      values = dtix.values.copy()
      values[dtix.weekday == 6] += np.timedelta64(1, 'D')
      return pd.DatetimeIndex(values)
docs: A vectorized implementation of
      :func:`pandas.tseries.holiday.sunday_to_monday`.
  
      Parameters
      ----------
      dtix : pd.DatetimeIndex
          The index to shift sundays to mondays.
  
      Returns
      -------
      sundays_as_mondays : pd.DatetimeIndex
          ``dtix`` with all sundays moved to the next monday.