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
919595236,MDExOlB1bGxSZXF1ZXN0NjY4ODk3OTc0,5464,Allow plotting categorical data,14371165,closed,0,,,3,2021-06-12T15:51:34Z,2021-07-18T21:19:21Z,2021-06-21T17:45:39Z,MEMBER,,0,pydata/xarray/pulls/5464,"<!-- Feel free to remove check-list items aren't relevant to your change -->

- [x] Closes #4260
- [x] Tests added
- [x] Passes `pre-commit run --all-files`
- [x] User visible changes (including notable bug fixes) are documented in `whats-new.rst`


```python
a = xr.DataArray(
    [0, 1, 2],
    dims=(""dim_1""),
    coords=dict(dim_1=([""dim_1""], [""u"", ""v"", ""w""])),
)
a.plot()
```
![image](https://user-images.githubusercontent.com/14371165/121782053-0a23e180-cba8-11eb-9524-46bfe8c94b35.png)


```python
a = xr.DataArray(
    [[0, 1, 2], [3, 4, 5]],
    dims=(""dim_0"", ""dim_1""),
    coords=dict(dim_0=([""dim_0""], [0, 1]), dim_1=([""dim_1""], [""u"", ""v"", ""w""])),
)
a.plot()
```
![image](https://user-images.githubusercontent.com/14371165/121781955-89fd7c00-cba7-11eb-8032-9b562f288621.png)
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