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
830930964,MDU6SXNzdWU4MzA5MzA5NjQ=,5032,Error when using xarray where that results in zero dimensions. ,5339008,closed,0,,,4,2021-03-13T16:09:30Z,2021-04-19T02:48:39Z,2021-04-19T02:48:38Z,NONE,,,,"Xarray 0.17.0

Executing the following code: 

```python
import xarray as xray

ncurl='http://tds.coaps.fsu.edu/thredds/dodsC/samos/data/intermediate/ZMFR/2021/ZMFR_20210303v20001.nc'
dat =xray.open_dataset(ncurl)
#dat=dat.where(dat.lat>-90.0,drop=True)
dat=dat.where(dat.lat>-11.0,drop=True)
dat=dat.where(dat.lat<30.0,drop=True)
dat=dat.where(dat.lon>91.0,drop=True)
dat=dat.where(dat.lon<139.0,drop=True)
print(dat)
```

Results in the error:

```python
Traceback (most recent call last):
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/backends/netCDF4_.py"", line 98, in _getitem
    array = getitem(original_array, key)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/backends/common.py"", line 53, in robust_getitem
    return array[key]
  File ""src/netCDF4/_netCDF4.pyx"", line 4397, in netCDF4._netCDF4.Variable.__getitem__
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/netCDF4/utils.py"", line 467, in _out_array_shape
    c = count[..., i].ravel()[0] # All elements should be identical.
IndexError: index 0 is out of bounds for axis 0 with size 0

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ""./test_xarray_error.py"", line 7, in <module>
    dat=dat.where(dat.lat>-11.0,drop=True)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/common.py"", line 1273, in where
    return ops.where_method(self, cond, other)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/ops.py"", line 195, in where_method
    return apply_ufunc(
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/computation.py"", line 1116, in apply_ufunc
    return apply_dataset_vfunc(
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/computation.py"", line 428, in apply_dataset_vfunc
    result_vars = apply_dict_of_variables_vfunc(
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/computation.py"", line 373, in apply_dict_of_variables_vfunc
    result_vars[name] = func(*variable_args)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/computation.py"", line 628, in apply_variable_ufunc
    input_data = [
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/computation.py"", line 629, in <listcomp>
    broadcast_compat_data(arg, broadcast_dims, core_dims)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/computation.py"", line 542, in broadcast_compat_data
    data = variable.data
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/variable.py"", line 374, in data
    return self.values
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/variable.py"", line 554, in values
    return _as_array_or_item(self._data)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/variable.py"", line 287, in _as_array_or_item
    data = np.asarray(data)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/numpy/core/_asarray.py"", line 102, in asarray
    return array(a, dtype, copy=False, order=order)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/indexing.py"", line 693, in __array__
    self._ensure_cached()
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/indexing.py"", line 690, in _ensure_cached
    self.array = NumpyIndexingAdapter(np.asarray(self.array))
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/numpy/core/_asarray.py"", line 102, in asarray
    return array(a, dtype, copy=False, order=order)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/indexing.py"", line 663, in __array__
    return np.asarray(self.array, dtype=dtype)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/numpy/core/_asarray.py"", line 102, in asarray
    return array(a, dtype, copy=False, order=order)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/indexing.py"", line 568, in __array__
    return np.asarray(array[self.key], dtype=None)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/coding/strings.py"", line 236, in __getitem__
    return _numpy_char_to_bytes(self.array[key])
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/coding/strings.py"", line 193, in _numpy_char_to_bytes
    arr = np.array(arr, copy=False, order=""C"")
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/indexing.py"", line 568, in __array__
    return np.asarray(array[self.key], dtype=None)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/backends/netCDF4_.py"", line 85, in __getitem__
    return indexing.explicit_indexing_adapter(
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/core/indexing.py"", line 853, in explicit_indexing_adapter
    result = raw_indexing_method(raw_key.tuple)
  File ""/home/hunter/miniconda3/lib/python3.8/site-packages/xarray/backends/netCDF4_.py"", line 108, in _getitem
    raise IndexError(msg)
IndexError: The indexing operation you are attempting to perform is not valid on netCDF4.Variable object. Try loading your data into memory first by calling .load().
```

It seems to be related to the fact that: 
`dat=dat.where(dat.lat>-11.0,drop=True)`
results in a zero dimension (time). 

However, if I uncomment one line and run:

```python
import xarray as xray


ncurl='http://tds.coaps.fsu.edu/thredds/dodsC/samos/data/intermediate/ZMFR/2021/ZMFR_20210303v20001.nc'
dat =xray.open_dataset(ncurl)
dat=dat.where(dat.lat>-90.0,drop=True)
dat=dat.where(dat.lat>-11.0,drop=True)
dat=dat.where(dat.lat<30.0,drop=True)
dat=dat.where(dat.lon>91.0,drop=True)
dat=dat.where(dat.lon<139.0,drop=True)
print(dat)
```

There is no error, even though the line with `dat=dat.where(dat.lat>-11.0,drop=True)` still results in a zero dimension. 

Perhaps this is not a bug, but maybe I am misunderstanding how where() works in xarray. But it seems inconsistent. 

Eli Hunter
Rutgers University","{""url"": ""https://api.github.com/repos/pydata/xarray/issues/5032/reactions"", ""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,completed,13221727,issue