html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/2148#issuecomment-747391520,https://api.github.com/repos/pydata/xarray/issues/2148,747391520,MDEyOklzc3VlQ29tbWVudDc0NzM5MTUyMA==,35919497,2020-12-17T11:47:44Z,2020-12-17T11:47:44Z,COLLABORATOR,I think this has been fixed at some point. it can be closed.,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,324032926
https://github.com/pydata/xarray/issues/2148#issuecomment-389935163,https://api.github.com/repos/pydata/xarray/issues/2148,389935163,MDEyOklzc3VlQ29tbWVudDM4OTkzNTE2Mw==,35919497,2018-05-17T16:52:16Z,2018-05-17T17:27:07Z,COLLABORATOR,"The coordinates are grouped correctly:
```python
list(arr.groupby('x'))

[(1, <xarray.DataArray (x: 3)>
  array([1., 1., 1.])
  Coordinates:
    * x        (x) int64 1 1 1
      x2       (x) int64 1 2 3), 
(2, <xarray.DataArray (x: 2)>
  array([1., 1.])
  Coordinates:
    * x        (x) int64 2 2
      x2       (x) int64 4 5)]
```
I think the grouping make sense. But once the groups are collapsed with some operation, I'm not sure that can be found a corresponding meaningful operation to apply to the grouped coordinates. 

In the following cases the mean after gourpby() works as expected:

```
arr = xr.DataArray(
    np.ones(5), 
    dims=('x',), 
    coords={
        'x': ('x', np.array([1, 1, 1, 2, 2])),
        'x1': ('x', np.array([1, 1, 1, 2, 2])),
        'x2': ('x', np.array([1, 2, 3, 4, 5])),

    }
)

arr.groupby('x1').mean('x')

<xarray.DataArray (x1: 2)>
array([1., 1.])
Coordinates:
  * x1       (x1) int64 1 2

arr.groupby((xr.DataArray([1,1,1,2,2], dims=('x'), name='x3'))).mean('x')

<xarray.DataArray (x3: 2)>
array([1., 1.])
Coordinates:
  * x3       (x3) int64 1 2
```
Also also if I try to group with an array named with as the dimension along which we perform the mean,  I get the same problem:
```python
arr.groupby(xr.DataArray([1,1,1,2,2], dims=('x'), name='x')).mean('x')

<xarray.DataArray (x: 2)>
array([1., 1.])
Coordinates:
  * x        (x) int64 1 2
    x1       (x) int64 1 1 1 2 2
    x2       (x) int64 1 2 3 4 5
```

If I try to use an other dimension name we obtain again an strange behaviour:
```python
arr = xr.DataArray(
    np.ones((5, 2)), 
    dims=('x', 'y'), 
    coords={
        'x': ('x', np.array([1, 1, 1, 2, 2])),
        'x1': ('x', np.array([1, 1, 1, 2, 2])),
        'x2': ('x', np.array([1, 2, 3, 4, 5])),
    }
)

arr.groupby(xr.DataArray([1,1,1,2,2], dims=('x'), name='y')).mean('x')

<xarray.DataArray (y: 4)>
array([1., 1., 1., 1.])
Coordinates:
  * y        (y) int64 1 2

```
In this case probably it should raise an error. ","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,324032926