Make cftime dateoffsets public #5687
Description
Consider the following cftime vector. It's fairly common to see users asking how to subtract "1 month" from this kind of vector:
xr.set_options(display_style="text")
time = xr.DataArray(
xr.cftime_range("1000-01-01", "1000-05-01", freq="MS", calendar="360_day"), dims="time", name="time"
)
time<xarray.DataArray 'time' (time: 5)>
array([cftime.Datetime360Day(1000, 1, 1, 0, 0, 0, 0, has_year_zero=False),
cftime.Datetime360Day(1000, 2, 1, 0, 0, 0, 0, has_year_zero=False),
cftime.Datetime360Day(1000, 3, 1, 0, 0, 0, 0, has_year_zero=False),
cftime.Datetime360Day(1000, 4, 1, 0, 0, 0, 0, has_year_zero=False),
cftime.Datetime360Day(1000, 5, 1, 0, 0, 0, 0, has_year_zero=False)],
dtype=object)
Coordinates:
* time (time) object 1000-01-01 00:00:00 ... 1000-05-01 00:00:00
Subtracting pd.Timedelta("1 month") does not work because a month does not represent an absolute unit of time. Instead the solution appears to be:
time - xr.coding.cftime_offsets.MonthBegin(1)<xarray.DataArray 'time' (time: 5)>
array([cftime.Datetime360Day(999, 12, 1, 0, 0, 0, 0, has_year_zero=False),
cftime.Datetime360Day(1000, 1, 1, 0, 0, 0, 0, has_year_zero=False),
cftime.Datetime360Day(1000, 2, 1, 0, 0, 0, 0, has_year_zero=False),
cftime.Datetime360Day(1000, 3, 1, 0, 0, 0, 0, has_year_zero=False),
cftime.Datetime360Day(1000, 4, 1, 0, 0, 0, 0, has_year_zero=False)],
dtype=object)
Coordinates:
* time (time) object 1000-01-01 00:00:00 ... 1000-05-01 00:00:00
I think pandas exposes this functionality as pd.DateOffset(months=1). Can we add a similar xr.DateOffset?