issues: 1923361961

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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
1923361961 I_kwDOAMm_X85ypCyp 8263 Surprising `.groupby` behavior with float index 5635139 closed 0     0 2023-10-03T05:50:49Z 2024-01-08T01:05:25Z 2024-01-08T01:05:25Z MEMBER      

What is your issue?

We raise an error on grouping without supplying dims, but not for float indexes — is this intentional or an oversight?

This is without flox installed

```python

da = xr.tutorial.open_dataset("air_temperature")['air']

da.drop_vars('lat').groupby('lat').sum() ```

```

ValueError Traceback (most recent call last) Cell In[8], line 1 ----> 1 da.drop_vars('lat').groupby('lat').sum() ... ValueError: cannot reduce over dimensions ['lat']. expected either '...' to reduce over all dimensions or one or more of ('time', 'lon'). ```

But with a float index, we don't raise:

python da.groupby('lat').sum()

...returns the original array:

Out[15]: <xarray.DataArray 'air' (time: 2920, lat: 25, lon: 53)> array([[[296.29 , 296.79 , 297.1 , ..., 296.9 , 296.79 , 296.6 ], [295.9 , 296.19998, 296.79 , ..., 295.9 , 295.9 , 295.19998], [296.6 , 296.19998, 296.4 , ..., 295.4 , 295.1 , 294.69998], ...

And if we try this with a non-float index, we get the error again:

python da.groupby('time').sum()

ValueError: cannot reduce over dimensions ['time']. expected either '...' to reduce over all dimensions or one or more of ('lat', 'lon').

 
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