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/3390#issuecomment-788507019,https://api.github.com/repos/pydata/xarray/issues/3390,788507019,MDEyOklzc3VlQ29tbWVudDc4ODUwNzAxOQ==,2448579,2021-03-02T01:42:09Z,2021-03-02T01:42:09Z,MEMBER,"> It seems rather unlikely to me to have an example of where with drop=True where the condition is exactly aligned with the grid, such that there are no missing values.

Actually, this is a really common pattern
``` python
ds = xr.tutorial.open_dataset('air_temperature')
ds.where(ds.time.dt.hour.isin([0, 12]), drop=True)
```

The efficient way to do this is
``` python
ds.loc[{""time"": ds.time.dt.hour.isin([0, 12])}]
```
or 

``` python
ds.sel(time=ds.time.dt.hour.isin([0, 12]))
```

At this point
https://github.com/pydata/xarray/blob/48378c4b11c5c2672ff91396d4284743165b4fbe/xarray/core/common.py#L1270-L1273

`cond` is all `True` and applying `where` is basically a totally useless copy since the `isel` has already copied.

Shall we raise a warning in `where` advising the more-efficient syntax? Or shall we skip the call to `where_method`","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,505493879
https://github.com/pydata/xarray/issues/3390#issuecomment-542945576,https://api.github.com/repos/pydata/xarray/issues/3390,542945576,MDEyOklzc3VlQ29tbWVudDU0Mjk0NTU3Ng==,2448579,2019-10-17T00:32:08Z,2019-10-17T00:32:08Z,MEMBER,Looks great. You did well!,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,505493879
https://github.com/pydata/xarray/issues/3390#issuecomment-541106974,https://api.github.com/repos/pydata/xarray/issues/3390,541106974,MDEyOklzc3VlQ29tbWVudDU0MTEwNjk3NA==,2448579,2019-10-11T15:16:48Z,2019-10-11T15:16:48Z,MEMBER,@pmallas it would be nice to update the docstring to make that clear if you are up for it,"{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,505493879