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