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.

def vectorized_sunday_to_monday(dtix):
    """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.
    """
    values = dtix.values.copy()
    values[dtix.weekday == 6] += np.timedelta64(1, 'D')
    return pd.DatetimeIndex(values)