issues: 965072308

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
965072308 MDU6SXNzdWU5NjUwNzIzMDg= 5687 Make cftime dateoffsets public 2448579 open 0     2 2021-08-10T14:57:39Z 2021-08-10T23:28:20Z   MEMBER      

Consider the following cftime vector. It's fairly common to see users asking how to subtract "1 month" from this kind of vector:

python 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: python 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?

 
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