issues: 324272267

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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
324272267 MDU6SXNzdWUzMjQyNzIyNjc= 2157 groupby should not squeeze out dimensions 35919497 closed 0     1 2018-05-18T05:10:57Z 2024-01-08T01:05:24Z 2024-01-08T01:05:24Z COLLABORATOR      

Code Sample

```python arr = xr.DataArray( np.ones(3), dims=('x',), coords={ 'x': ('x', np.array([1, 3, 6])), } ) list(arr.groupby('x'))

[(1, <xarray.DataArray ()> array(1.) Coordinates: x int64 1), (3, <xarray.DataArray ()> array(1.) Coordinates: x int64 3), (6, <xarray.DataArray ()> array(1.) Coordinates: x int64 6)] ```

Problem description

The dimension x disappear. I have done some tests and it seems that this problem raise only with strictly ascending coordinates. For example in this case it works correctly:

```python arr = xr.DataArray( np.ones(3), dims=('x',), coords={ 'x': ('x', np.array([2, 1, 0])), } ) list(arr.groupby('x'))

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

Expected Output

```python arr = xr.DataArray( np.ones(3), dims=('x',), coords={ 'x': ('x', np.array([1, 3, 6])), } ) list(arr.groupby('x'))

[(1, <xarray.DataArray (x: 1)> ar1ay([1.]) Coordinates: * x (x) int64 1), (3, <xarray.DataArray (x: 1)> array([1.]) Coordinates: * x (x) int64 3), (6, <xarray.DataArray (x: 1)> array([1.]) Coordinates: * x (x) int64 6)] ```

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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