issues: 569408125

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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
569408125 MDExOlB1bGxSZXF1ZXN0Mzc4NjQyMTE5 3792 Enable pandas-style rounding of cftime.datetime objects 6628425 closed 0     1 2020-02-22T23:26:50Z 2020-03-02T12:03:47Z 2020-03-02T09:41:20Z MEMBER   0 pydata/xarray/pulls/3792
  • [x] Tests added
  • [x] Passes isort -rc . && black . && mypy . && flake8
  • [x] Fully documented, including whats-new.rst for all changes and api.rst for new API

This is particularly useful for removing microsecond noise that can sometimes be added from decoding times via cftime.num2date, though also applies more generally. The methods used here for rounding dates in the integer domain are copied from pandas.

On a somewhat more internal note, this adds an asi8 property to CFTimeIndex, which encodes the dates as integer values representing microseconds since 1970-01-01; this encoding is made exact via the exact_cftime_datetime_difference function. It's possible this could be useful in other contexts.

Some examples:

``` In [1]: import xarray as xr

In [2]: times = xr.cftime_range("2000", periods=5, freq="17D")

In [3]: time = xr.DataArray(times, dims=["time"], name="time")

In [4]: time.dt.floor("11D") Out[4]: <xarray.DataArray 'floor' (time: 5)> array([cftime.DatetimeGregorian(1999-12-31 00:00:00), cftime.DatetimeGregorian(2000-01-11 00:00:00), cftime.DatetimeGregorian(2000-02-02 00:00:00), cftime.DatetimeGregorian(2000-02-13 00:00:00), cftime.DatetimeGregorian(2000-03-06 00:00:00)], dtype=object) Coordinates: * time (time) object 2000-01-01 00:00:00 ... 2000-03-09 00:00:00

In [5]: time.dt.ceil("11D") Out[5]: <xarray.DataArray 'ceil' (time: 5)> array([cftime.DatetimeGregorian(2000-01-11 00:00:00), cftime.DatetimeGregorian(2000-01-22 00:00:00), cftime.DatetimeGregorian(2000-02-13 00:00:00), cftime.DatetimeGregorian(2000-02-24 00:00:00), cftime.DatetimeGregorian(2000-03-17 00:00:00)], dtype=object) Coordinates: * time (time) object 2000-01-01 00:00:00 ... 2000-03-09 00:00:00

In [6]: time.dt.round("11D") Out[6]: <xarray.DataArray 'round' (time: 5)> array([cftime.DatetimeGregorian(1999-12-31 00:00:00), cftime.DatetimeGregorian(2000-01-22 00:00:00), cftime.DatetimeGregorian(2000-02-02 00:00:00), cftime.DatetimeGregorian(2000-02-24 00:00:00), cftime.DatetimeGregorian(2000-03-06 00:00:00)], dtype=object) Coordinates: * time (time) object 2000-01-01 00:00:00 ... 2000-03-09 00:00:00 ```

 
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