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
1268697316,PR_kwDOAMm_X845hhHE,6690,Fix Dataset.where with drop=True and mixed dims,43316012,closed,0,,,3,2022-06-12T20:47:05Z,2022-06-13T18:06:44Z,2022-06-12T22:06:51Z,COLLABORATOR,,0,pydata/xarray/pulls/6690,"- [x] Closes #6227
- [x] Tests added
- [x] User visible changes (including notable bug fixes) are documented in `whats-new.rst`
","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6690/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,,13221727,pull
1120378011,I_kwDOAMm_X85Cx5yb,6227,"[Bug]: Dataset.where(x, drop=True) behaves inconsistent",43316012,closed,0,,,0,2022-02-01T08:40:30Z,2022-06-12T22:06:51Z,2022-06-12T22:06:51Z,COLLABORATOR,,,,"### What happened?

I tried to reduce some dimensions using where (sel did not work in this case) and shorten the dimensions with ""drop=True"".
This works fine on DataArrays and Datasets with only a single dimension but fails as soon as you have a Dataset with two dimensions on different variables.
The dimensions are left untouched and you have NaNs in the data, just as if you were using ""drop=False"" (see example).

I am actually not sure what the expected behavior is, maybe I am wrong and it is correct due to some broadcasting rules?

### What did you expect to happen?

I expected that relevant dims are shortened.
If the `ds.where` with ""drop=False"" all variables along a dimenions have some NaNs, then using ""drop=True"" I expect these dimensions to be shortened and the NaNs removed.

### Minimal Complete Verifiable Example

```python
import xarray as xr

# this works
ds = xr.Dataset({""a"": (""x"", [1, 2 ,3])})
ds.where(ds > 2, drop=True)

# returns:
# <xarray.Dataset>
# Dimensions:  (x: 1)
# Dimensions without coordinates: x
# Data variables:
#     a        (x) float64 3.0

# this doesn't
ds = xr.Dataset({""a"": (""x"", [1, 2 ,3]), ""b"": (""y"", [2, 3, 4])})
ds.where(ds > 2, drop=True)

# returns:
# <xarray.Dataset>
# Dimensions:  (x: 3, y: 3)
# Dimensions without coordinates: x, y
# Data variables:
#     a        (x) float64 nan nan 3.0
#     b        (y) float64 nan 3.0 4.0
```


### Relevant log output

_No response_

### Anything else we need to know?

_No response_

### Environment

INSTALLED VERSIONS
------------------
commit: None
python: 3.9.1 (default, Jan 13 2021, 15:21:08) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-44)]
python-bits: 64
OS: Linux
OS-release: 3.10.0-1160.49.1.el7.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: ('en_US', 'UTF-8')
libhdf5: 1.12.0
libnetcdf: 4.7.4

xarray: 0.20.2
pandas: 1.3.5
numpy: 1.21.5
scipy: 1.7.3
netCDF4: 1.5.8
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.5.1.1
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: None
distributed: None
matplotlib: 3.5.1
cartopy: None
seaborn: None
numbagg: None
fsspec: None
cupy: None
pint: None
sparse: None
setuptools: 49.2.1
pip: 22.0.2
conda: None
pytest: 6.2.5
IPython: 8.0.0
sphinx: None","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/6227/reactions"", ""total_count"": 2, ""+1"": 2, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue