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/3954#issuecomment-610707359,https://api.github.com/repos/pydata/xarray/issues/3954,610707359,MDEyOklzc3VlQ29tbWVudDYxMDcwNzM1OQ==,6815844,2020-04-08T01:53:23Z,2020-04-08T01:53:23Z,MEMBER,"Ah, OK. Makes sense. Thanks.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,596249070
https://github.com/pydata/xarray/issues/3954#issuecomment-610705859,https://api.github.com/repos/pydata/xarray/issues/3954,610705859,MDEyOklzc3VlQ29tbWVudDYxMDcwNTg1OQ==,6815844,2020-04-08T01:48:23Z,2020-04-08T01:48:23Z,MEMBER,"Hi, @zxdawn 

Thank you for raising the issue.
I think you need an actual value of `z` as your `b.expand_dims('z')` does not have a value for `z` but it only knows the `z` is the dimension name.

You can do like
```python
b['z'] = 3  # add a scalar coordinate named 'z'
```
to add a value (we call it `coordinate`) for `z`
Then, your script will work,
```
b = b.expand_dims('z')  # expand 2d to 3d
comb = xr.concat([a, b], dim='z')
```

","{""total_count"": 2, ""+1"": 2, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,596249070