issues: 324121124

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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
324121124 MDU6SXNzdWUzMjQxMjExMjQ= 2153 Bug: side effect on method GroupBy.first 35919497 closed 0     1 2018-05-17T17:43:25Z 2018-05-29T03:15:08Z 2018-05-29T03:15:08Z COLLABORATOR      

Code Sample, a copy-pastable example if possible

```python arr = xr.DataArray( np.arange(5), dims=('x',), coords={ 'x': ('x', np.array([1, 1, 1, 2, 2])), } )

gr = arr.groupby('x') gr.first()

arr

<xarray.DataArray (x: 5)> array([0, 1, 2, 3, 4]) Coordinates: * x (x) int64 1 2

```

Problem description

A side effect of the GroupBy.first method call is that it substitutes the original array coordinates with the grouped ones .

Expected Output

arr

<xarray.DataArray (x: 5)> array([0, 1, 2, 3, 4]) Coordinates: * x (x) int64 1 1 1 2 2

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.6.0.final.0 python-bits: 64 OS: Linux OS-release: 4.13.0-41-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 xarray: 0.10.4 pandas: 0.22.0 numpy: 1.14.3 scipy: 1.1.0 netCDF4: 1.3.1 h5netcdf: None h5py: 2.7.1 Nio: None zarr: None bottleneck: None cyordereddict: None dask: 0.17.4 distributed: 1.21.8 matplotlib: 2.2.2 cartopy: 0.16.0 seaborn: None setuptools: 38.4.1 pip: 10.0.1 conda: None pytest: 3.5.1 IPython: 6.2.1 sphinx: 1.7.4 
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   completed 13221727 issue

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