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
484270833,MDU6SXNzdWU0ODQyNzA4MzM=,3248,combine_by_coords fails with DataArrays,2448579,closed,0,,,11,2019-08-23T00:11:38Z,2021-07-02T21:34:36Z,2021-07-02T21:34:36Z,MEMBER,,,,"#### MCVE Code Sample
<!-- In order for the maintainers to efficiently understand and prioritize issues, we ask you post a ""Minimal, Complete and Verifiable Example"" (MCVE): http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports -->

```python
da1 = xr.DataArray([1, 2, 3], dims='x', coords={'x': [0, 1, 2]})
da2 = xr.DataArray([3, 4, 5], dims='x', coords={'x': [2, 3, 4]})
xr.combine_by_coords([da1, da2])
```

```
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-133-d27216ba5688> in <module>
      1 da1 = xr.DataArray([1, 2, 3], dims='x', coords={'x': [0, 1, 2]})
      2 da2 = xr.DataArray([3, 4, 5], dims='x', coords={'x': [2, 3, 4]})
----> 3 xr.combine_by_coords([da1, da2])

~/work/python/xarray/xarray/core/combine.py in combine_by_coords(datasets, compat, data_vars, coords, fill_value, join)
    619         compat=compat,
    620         fill_value=fill_value,
--> 621         join=join,
    622     )
    623 

~/work/python/xarray/xarray/core/merge.py in merge(objects, compat, join, fill_value)
    588             )
    589 
--> 590         obj = obj.to_dataset() if isinstance(obj, DataArray) else obj
    591         dict_like_objects.append(obj)
    592 

~/work/python/xarray/xarray/core/dataarray.py in to_dataset(self, dim, name)
    478             return self._to_dataset_split(dim)
    479         else:
--> 480             return self._to_dataset_whole(name)
    481 
    482     @property

~/work/python/xarray/xarray/core/dataarray.py in _to_dataset_whole(self, name, shallow_copy)
    426         if name is None:
    427             raise ValueError(
--> 428                 ""unable to convert unnamed DataArray to a ""
    429                 ""Dataset without providing an explicit name""
    430             )

ValueError: unable to convert unnamed DataArray to a Dataset without providing an explicit name
```

To get what I want, I need
```xr.combine_by_coords([da1.to_dataset(name='a'), da2.to_dataset(name='a')]).a```

I think the issue is that the code uses `to_dataset` instead of `_to_temp_dataset`
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/3248/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue
484639035,MDExOlB1bGxSZXF1ZXN0MzEwNDc1MzIy,3255,Sparse fixes for reindex,2448579,closed,0,,,2,2019-08-23T17:39:08Z,2019-08-27T00:00:48Z,2019-08-27T00:00:44Z,MEMBER,,0,pydata/xarray/pulls/3255,"<!-- Feel free to remove check-list items aren't relevant to your change -->

 - [x] Tests added
 - [x] Passes `black . && mypy . && flake8`
 - [x] Fully documented, including `whats-new.rst` for all changes and `api.rst` for new API
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/3255/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull