如何更正Xarray数据集中的坐标元数据属性如时间日历？

如何解决如何更正Xarray数据集中的坐标元数据属性如时间日历？

不幸的是，我正在读入xarray的NetCDF文件在指定为gregorian_proleptic而不是CF标准proleptic_gregorian的时间坐标上具有calendar属性。

我该如何解决？

我尝试仅更改属性，但是xarray必须将元数据保存在我需要修改的其他位置，因为当我尝试使用decode_cf时，它仍然认为日历为gregorian_proleptic。这是我尝试过的：

import xarray as xr
import fsspec

url='s3://noaa-ofs-pds/dbofs.20200826/nos.dbofs.fields.f044.20200826.t06z.nc'
ncfile = fsspec.open(url)
ds = xr.open_dataset(ncfile.open(),decode_times=False)

ds.ocean_time.attrs['calendar']='proleptic_gregorian'

xr.decode_cf(ds,decode_times=True)

产生：

---------------------------------------------------------------------------
OutOfBoundsDatetime                       Traceback (most recent call last)
/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/coding/times.py in decode_cf_datetime(num_dates,units,calendar,use_cftime)
    157         try:
--> 158             dates = _decode_datetime_with_pandas(flat_num_dates,calendar)
    159         except (KeyError,OutOfBoundsDatetime,OverflowError):

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/coding/times.py in _decode_datetime_with_pandas(flat_num_dates,calendar)
    105             "Cannot decode times from a non-standard calendar,{!r},using "
--> 106             "pandas.".format(calendar)
    107         )

OutOfBoundsDatetime: Cannot decode times from a non-standard calendar,'gregorian_proleptic',using pandas.

During handling of the above exception,another exception occurred:

KeyError                                  Traceback (most recent call last)
/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/coding/times.py in _decode_cf_datetime_dtype(data,use_cftime)
     76     try:
---> 77         result = decode_cf_datetime(example_value,use_cftime)
     78     except Exception:

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/coding/times.py in decode_cf_datetime(num_dates,use_cftime)
    160             dates = _decode_datetime_with_cftime(
--> 161                 flat_num_dates.astype(float),calendar
    162             )

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/coding/times.py in _decode_datetime_with_cftime(num_dates,calendar)
     97     return np.asarray(
---> 98         cftime.num2date(num_dates,only_use_cftime_datetimes=True)
     99     )

cftime/_cftime.pyx in cftime._cftime.num2date()

cftime/_cftime.pyx in cftime._cftime.to_calendar_specific_datetime()

KeyError: 'gregorian_proleptic'

During handling of the above exception,another exception occurred:

ValueError                                Traceback (most recent call last)
<ipython-input-41-174237fc09de> in <module>
----> 1 xr.decode_cf(ds,decode_times=True)

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/conventions.py in decode_cf(obj,concat_characters,mask_and_scale,decode_times,decode_coords,drop_variables,use_cftime,decode_timedelta)
    594         drop_variables=drop_variables,595         use_cftime=use_cftime,--> 596         decode_timedelta=decode_timedelta,597     )
    598     ds = Dataset(vars,attrs=attrs)

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/conventions.py in decode_cf_variables(variables,attributes,decode_timedelta)
    496             stack_char_dim=stack_char_dim,497             use_cftime=use_cftime,--> 498             decode_timedelta=decode_timedelta,499         )
    500         if decode_coords:

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/conventions.py in decode_cf_variable(name,var,decode_endianness,stack_char_dim,decode_timedelta)
    336         var = times.CFtimedeltaCoder().decode(var,name=name)
    337     if decode_times:
--> 338         var = times.CFDatetimeCoder(use_cftime=use_cftime).decode(var,name=name)
    339 
    340     dimensions,data,encoding = variables.unpack_for_decoding(var)

/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/coding/times.py in decode(self,variable,name)
    425             units = pop_to(attrs,encoding,"units")
    426             calendar = pop_to(attrs,"calendar")
--> 427             dtype = _decode_cf_datetime_dtype(data,self.use_cftime)
    428             transform = partial(
    429                 decode_cf_datetime,/srv/conda/envs/notebook/lib/python3.7/site-packages/xarray/coding/times.py in _decode_cf_datetime_dtype(data,use_cftime)
     85             "if it is not installed."
     86         )
---> 87         raise ValueError(msg)
     88     else:
     89         dtype = getattr(result,"dtype",np.dtype("object"))

ValueError: unable to decode time units 'days since 2016-01-01 00:00:00' with "calendar 'gregorian_proleptic'". Try opening your dataset with decode_times=False or installing cftime if it is not installed.

如果有用的话，这里是full notebook。

解决方法

有问题的数据集中还有另一个非坐标变量（dstart），该变量也具有错误的gregorian_proleptic日历属性。

如果设置正确：

ds.dstart.attrs['calendar']='proleptic_gregorian'
xr.decode_cf(ds,decode_times=True)

cf解码将起作用。