issues: 490476815

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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
490476815 MDU6SXNzdWU0OTA0NzY4MTU= 3287 GroupBy of stacked dim with strings renames underlying dims 1053153 closed 0     7 2019-09-06T18:59:47Z 2020-03-31T16:10:10Z 2020-03-31T16:10:10Z CONTRIBUTOR      

Names for dimensions are lost (renamed) when they are stacked and grouped, if one of the dimensions has string coordinates.

```python data = np.zeros((2,1,1)) dims = ['c', 'y', 'x']

d1 = xr.DataArray(data, dims=dims) g1 = d1.stack(f=['c', 'x']).groupby('f').first() print('Expected dim names:') print(g1.coords) print()

d2 = xr.DataArray(data, dims=dims, coords={'c': ['R', 'G']}) g2 = d2.stack(f=['c', 'x']).groupby('f').first() print('Unexpected dim names:') print(g2.coords) ```

Output

It is expected the 'f_level_0' and 'f_level_1' be 'c' and 'x', respectively in the second part below. ``` Expected dim names: Coordinates: * f (f) MultiIndex - c (f) int64 0 1 - x (f) int64 0 0

Unexpected dim names: Coordinates: * f (f) MultiIndex - f_level_0 (f) object 'G' 'R' - f_level_1 (f) int64 0 0 ```

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.7.4 (default, Jul 9 2019, 18:13:23) [Clang 10.0.1 (clang-1001.0.46.4)] python-bits: 64 OS: Darwin OS-release: 18.7.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.2 libnetcdf: 4.6.3 xarray: 0.12.3 pandas: 0.25.1 numpy: 1.17.1 scipy: 1.3.1 netCDF4: 1.5.2 pydap: None h5netcdf: None h5py: 2.9.0 Nio: None zarr: None cftime: 1.0.3.4 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: None distributed: None matplotlib: 3.1.1 cartopy: None seaborn: None numbagg: None setuptools: 41.2.0 pip: 19.2.3 conda: None pytest: None IPython: 7.8.0 sphinx: None 
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