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/2834#issuecomment-499285779,https://api.github.com/repos/pydata/xarray/issues/2834,499285779,MDEyOklzc3VlQ29tbWVudDQ5OTI4NTc3OQ==,3621629,2019-06-05T22:56:00Z,2019-06-05T22:58:18Z,CONTRIBUTOR,"Hello @maxdow 

I'm not sure I understand your issue correctly. If all you want is to keep only the points `time, lat, lon` for which `t` and/or `dd` is not NA you can simply use
```python
z = d.stack(index=d.dims).dropna('index', how='all')

<xarray.Dataset>
Dimensions:  (index: 346)
Coordinates:
  * index    (index) MultiIndex
  - time     (index) datetime64[ns] 2019-03-09 2019-03-09 ... 2019-03-09
  - lat      (index) float64 43.5 43.5 43.5 43.75 43.75 ... 45.0 45.0 45.5 45.5
  - lon      (index) float64 1.25 1.5 4.25 1.75 2.25 ... 1.75 2.0 4.0 1.5 2.0
Data variables:
    t        (index) float64 0.6184 0.2966 1.426 0.8666 ... 0.09348 1.271 1.353
    dd       (index) float64 2.075 1.174 0.906 0.6451 ... 0.3491 0.1789 0.8922
```
You still have access to the coordinates of the valid points through `z.time`, `z.lat` and `z.lon`:
```python
z.lat

<xarray.DataArray 'lat' (index: 346)>
array([43.5 , 43.5 , 43.5 , ..., 51.25, 51.25, 51.25])
Coordinates:
  * index    (index) MultiIndex
  - time     (index) datetime64[ns] 2019-03-09 2019-03-09 ... 2019-03-09
  - lat      (index) float64 43.5 43.5 43.5 43.75 43.75 ... 45.0 45.0 45.5 45.5
  - lon      (index) float64 1.25 1.5 4.25 1.75 2.25 ... 1.75 2.0 4.0 1.5 2.0
```

One can still unstack this and achieve the equivalent of multi-dimensional dropna. However in your example all the coordinates for `time` look equal (they shouldn't be) and this will prevent unstacking.

I hope this helps


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