issues: 1367029446

What happened?

When performing a DataArray resampling on a time dimension, the metadata attributes of non-affected coordinate variables are dropped. This behaviour breaks compatibility with cf_xarray as the coordinate metadata is needed to identify the X, Y, Z coordinates.

What did you expect to happen?

Metadata fields of unaffected coordinates (lat, lon, height) to be preserved.

Minimal Complete Verifiable Example

```Python import xarray as xr import cf_xarray

ds = xr.open_dataset("my_dataset_that_has_lat_and_lon_coordinates.nc") tas = ds.tas.resample(time="MS").mean(dim="time")

tas.cf["latitude"] ```

MVCE confirmation

• [X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• [ ] Complete example — the example is self-contained, including all data and the text of any traceback.
• [ ] Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• [X] New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

```Python KeyError Traceback (most recent call last) File ~/mambaforge/envs/xclim310/lib/python3.10/site-packages/xarray/core/dataarray.py:760, in DataArray._getitem_coord(self, key) 759 try: --> 760 var = self._coords[key] 761 except KeyError:

KeyError: 'latitude'

During handling of the above exception, another exception occurred:

KeyError Traceback (most recent call last) File ~/mambaforge/envs/xclim310/lib/python3.10/site-packages/cf_xarray/accessor.py:706, in _getitem(accessor, key, skip) 705 for name in allnames: --> 706 extravars = accessor.get_associated_variable_names( 707 name, skip_bounds=scalar_key, error=False 708 ) 709 coords.extend(itertools.chain(*extravars.values()))

File ~/mambaforge/envs/xclim310/lib/python3.10/site-packages/cf_xarray/accessor.py:1597, in CFAccessor.get_associated_variable_names(self, name, skip_bounds, error) 1596 coords: dict[str, list[str]] = {k: [] for k in keys} -> 1597 attrs_or_encoding = ChainMap(self._obj[name].attrs, self._obj[name].encoding) 1599 if "coordinates" in attrs_or_encoding:

File ~/mambaforge/envs/xclim310/lib/python3.10/site-packages/xarray/core/dataarray.py:769, in DataArray.getitem(self, key) 768 if isinstance(key, str): --> 769 return self._getitem_coord(key) 770 else: 771 # xarray-style array indexing

File ~/mambaforge/envs/xclim310/lib/python3.10/site-packages/xarray/core/dataarray.py:763, in DataArray.getitem_coord(self, key) 762 dim_sizes = dict(zip(self.dims, self.shape)) --> 763 , key, var = _get_virtual_variable(self._coords, key, dim_sizes) 765 return self._replace_maybe_drop_dims(var, name=key)

File ~/mambaforge/envs/xclim310/lib/python3.10/site-packages/xarray/core/dataset.py:175, in _get_virtual_variable(variables, key, dim_sizes) 174 if len(split_key) != 2: --> 175 raise KeyError(key) 177 ref_name, var_name = split_key

KeyError: 'latitude'

During handling of the above exception, another exception occurred:

KeyError Traceback (most recent call last) Input In [7], in <cell line: 1>() ----> 1 tas.cf["latitude"]

File ~/mambaforge/envs/xclim310/lib/python3.10/site-packages/cf_xarray/accessor.py:2526, in CFDataArrayAccessor.getitem(self, key) 2521 if not isinstance(key, str): 2522 raise KeyError( 2523 f"Cannot use a list of keys with DataArrays. Expected a single string. Received {key!r} instead." 2524 ) -> 2526 return _getitem(self, key)

File ~/mambaforge/envs/xclim310/lib/python3.10/site-packages/cf_xarray/accessor.py:749, in _getitem(accessor, key, skip) 746 return ds.set_coords(coords) 748 except KeyError: --> 749 raise KeyError( 750 f"{kind}.cf does not understand the key {k!r}. " 751 f"Use 'repr({kind}.cf)' (or '{kind}.cf' in a Jupyter environment) to see a list of key names that can be interpreted." 752 )

KeyError: "DataArray.cf does not understand the key 'latitude'. Use 'repr(DataArray.cf)' (or 'DataArray.cf' in a Jupyter environment) to see a list of key names that can be interpreted." ```

Anything else we need to know?

Before

netcdf tas_Amon_CanESM2_rcp85_r1i1p1_200701-200712 { dimensions: time = UNLIMITED ; // (12 currently) bnds = 2 ; lat = 64 ; lon = 128 ; variables: double time(time) ; time:_FillValue = NaN ; time:bounds = "time_bnds" ; time:axis = "T" ; time:long_name = "time" ; time:standard_name = "time" ; time:units = "days since 1850-01-01" ; time:calendar = "365_day" ; double time_bnds(time, bnds) ; time_bnds:_FillValue = NaN ; time_bnds:coordinates = "height" ; double lat(lat) ; lat:_FillValue = NaN ; lat:bounds = "lat_bnds" ; lat:units = "degrees_north" ; lat:axis = "Y" ; lat:long_name = "latitude" ; lat:standard_name = "latitude" ; double lat_bnds(lat, bnds) ; lat_bnds:_FillValue = NaN ; lat_bnds:coordinates = "height" ; double lon(lon) ; lon:_FillValue = NaN ; lon:bounds = "lon_bnds" ; lon:units = "degrees_east" ; lon:axis = "X" ; lon:long_name = "longitude" ; lon:standard_name = "longitude" ; double lon_bnds(lon, bnds) ; lon_bnds:_FillValue = NaN ; lon_bnds:coordinates = "height" ; double height ; height:_FillValue = NaN ; height:units = "m" ; height:axis = "Z" ; height:positive = "up" ; height:long_name = "height" ; height:standard_name = "height" ; float tas(time, lat, lon) ; tas:_FillValue = 1.e+20f ; tas:standard_name = "air_temperature" ; tas:long_name = "Near-Surface Air Temperature" ; tas:units = "K" ; tas:original_name = "ST" ; tas:cell_methods = "time: mean (interval: 15 minutes)" ; tas:cell_measures = "area: areacella" ; tas:history = "2011-03-10T05:13:26Z altered by CMOR: Treated scalar dimension: \'height\'. 2011-03-10T05:13:26Z altered by CMOR: replaced missing value flag (1e+38) with standard missing value (1e+20)." ; tas:associated_files = "baseURL: http://cmip-pcmdi.llnl.gov/CMIP5/dataLocation gridspecFile: gridspec_atmos_fx_CanESM2_rcp85_r0i0p0.nc areacella: areacella_fx_CanESM2_rcp85_r0i0p0.nc" ; tas:coordinates = "height" ; tas:missing_value = 1.e+20f ;

After

netcdf test_cf_lat_new { dimensions: lat = 64 ; lon = 128 ; time = 11 ; variables: double lat(lat) ; lat:_FillValue = NaN ; double lon(lon) ; lon:_FillValue = NaN ; double height ; height:_FillValue = NaN ; height:units = "m" ; height:axis = "Z" ; height:positive = "up" ; height:long_name = "height" ; height:standard_name = "height" ; int64 time(time) ; time:units = "days since 2007-01-01 00:00:00.000000" ; time:calendar = "noleap" ; float tas(time, lat, lon) ; tas:_FillValue = NaNf ; tas:coordinates = "height" ;

Environment

INSTALLED VERSIONS ------------------ commit: None python: 3.10.5 | packaged by conda-forge | (main, Jun 14 2022, 07:06:46) [GCC 10.3.0] python-bits: 64 OS: Linux OS-release: 5.19.6-200.fc36.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_CA.UTF-8 LOCALE: ('en_CA', 'UTF-8') libhdf5: 1.12.1 libnetcdf: 4.8.1 xarray: 2022.6.0 pandas: 1.3.5 numpy: 1.22.4 scipy: 1.8.1 netCDF4: 1.6.0 pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: 1.6.2 nc_time_axis: 1.4.1 PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: 1.3.5 dask: 2022.6.1 distributed: 2022.6.1 matplotlib: 3.5.2 cartopy: None seaborn: None numbagg: None fsspec: 2022.7.1 cupy: None pint: 0.19.2 sparse: 0.13.0 flox: 0.5.10.dev8+gfbc2af8 numpy_groupies: 0.9.19 setuptools: 59.8.0 pip: 22.2.1 conda: None pytest: 7.1.2 IPython: 8.4.0 sphinx: 5.1.1