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Enable pandas-style rounding of cftime.datetime objects #3792

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Merged
dcherian merged 13 commits into from
Mar 2, 2020
Merged

Enable pandas-style rounding of cftime.datetime objects #3792

dcherian merged 13 commits into from
Mar 2, 2020

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@spencerkclark spencerkclark commented Feb 22, 2020 •
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  • Tests added
  • Passes isort -rc . && black . && mypy . && flake8
  • 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

dcherian
dcherian approved these changes Feb 24, 2020
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Thanks @spencerkclark

I had a couple of minor suggestions but looks great otherwise.

@spencerkclark
A couple cleanup items:
5ad10d7 
  - Fix floating point issue in asi8 and add tests
  - Ensure dask only computes once when using the rounding accessors
@spencerkclark
Merge branch 'master' into cftimeindex-round-floor-ceil
7ff0b4d
@spencerkclark
black
7f7e885
@spencerkclark
Merge branch 'master' into cftimeindex-round-floor-ceil
bc28dd2
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dcherian commented Mar 2, 2020

Thanks @spencerkclark

@dcherian dcherian merged commit 45d88fc into pydata:master Mar 2, 2020
@spencerkclark spencerkclark deleted the cftimeindex-round-floor-ceil branch March 2, 2020 12:03
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