What happened?

When setting axis limits is in matplotlib.:

ax.set_xlim(["2002-01-03","2002-01-20"])

A conversion error is raised.

IndexError Traceback (most recent call last) File C:\work\miniconda3\envs\XROMStest\lib\site-packages\matplotlib\axis.py:1507, in Axis.convert_units(self, x) 1506 try: -> 1507 ret = self.converter.convert(x, self.units, self) 1508 except Exception as e:

File C:\work\miniconda3\envs\XROMStest\lib\site-packages\matplotlib\dates.py:1921, in _SwitchableDateConverter.convert(self, args, kwargs) 1920 def convert(self, args, kwargs): -> 1921 return self._get_converter().convert(*args, kwargs)

File C:\work\miniconda3\envs\XROMStest\lib\site-packages\matplotlib\dates.py:1850, in DateConverter.convert(value, unit, axis) 1844 """ 1845 If value is not already a number or sequence of numbers, convert it 1846 with date2num. 1847 1848 The unit and axis arguments are not used. 1849 """ -> 1850 return date2num(value)

File C:\work\miniconda3\envs\XROMStest\lib\site-packages\matplotlib\dates.py:443, in date2num(d) 441 return d --> 443 tzi = getattr(d[0], 'tzinfo', None) 444 if tzi is not None: 445 # make datetime naive:

IndexError: too many indices for array: array is 0-dimensional, but 1 were indexed

The above exception was the direct cause of the following exception:

ConversionError Traceback (most recent call last) Input In [4], in <module> 10 fig, ax = plt.subplots() 11 ax.plot(times, y) ---> 12 ax.set_xlim(["2002-01-03","2002-01-20"])

File C:\work\miniconda3\envs\XROMStest\lib\site-packages\matplotlib\axes_base.py:3689, in _AxesBase.set_xlim(self, left, right, emit, auto, xmin, xmax) 3686 right = xmax 3688 self._process_unit_info([("x", (left, right))], convert=False) -> 3689 left = self._validate_converted_limits(left, self.convert_xunits) 3690 right = self._validate_converted_limits(right, self.convert_xunits) 3692 if left is None or right is None: 3693 # Axes init calls set_xlim(0, 1) before get_xlim() can be called, 3694 # so only grab the limits if we really need them.

File C:\work\miniconda3\envs\XROMStest\lib\site-packages\matplotlib\axes_base.py:3603, in _AxesBase._validate_converted_limits(self, limit, convert) 3592 """ 3593 Raise ValueError if converted limits are non-finite. 3594 (...) 3599 The limit value after call to convert(), or None if limit is None. 3600 """ 3601 if limit is not None: -> 3603 converted_limit = convert(limit) 3604 if (isinstance(converted_limit, Real) 3605 and not np.isfinite(converted_limit)): 3606 raise ValueError("Axis limits cannot be NaN or Inf")

File C:\work\miniconda3\envs\XROMStest\lib\site-packages\matplotlib\artist.py:252, in Artist.convert_xunits(self, x) 250 if ax is None or ax.xaxis is None: 251 return x --> 252 return ax.xaxis.convert_units(x)

File C:\work\miniconda3\envs\XROMStest\lib\site-packages\matplotlib\axis.py:1509, in Axis.convert_units(self, x) 1507 ret = self.converter.convert(x, self.units, self) 1508 except Exception as e: -> 1509 raise munits.ConversionError('Failed to convert value(s) to axis ' 1510 f'units: {x!r}') from e 1511 return ret

ConversionError: Failed to convert value(s) to axis units: '2002-01-03'

When we downgrade to xarray=0.20..2. axis limits are changed as expected.

What did you expect to happen?

ax.set_xlim should interpert dates of format "YYYY-MM-DD" correctly and scale the xaxis appropriately.

Minimal Complete Verifiable Example

```python import xarray as xr import numpy as np import matplotlib.pyplot as plt

times = np.arange(np.datetime64('2001-01-02'), np.datetime64('2002-02-03'), np.timedelta64(75, 'm')) y = np.random.randn(len(times))

fig, ax = plt.subplots() ax.plot(times, y) ax.set_xlim(["2002-01-03","2002-01-20"]) ```

Relevant log output

No response

Anything else we need to know?

It appears that matplotlib uses a pandas date converter when using xarray 0.20.2 is imported but not for xarray 0.21.1.

Environment

INSTALLED VERSIONS

commit: None python: 3.8.12 | packaged by conda-forge | (default, Oct 12 2021, 21:22:46) [MSC v.1916 64 bit (AMD64)] python-bits: 64 OS: Windows OS-release: 10 machine: AMD64 processor: Intel64 Family 6 Model 140 Stepping 1, GenuineIntel byteorder: little LC_ALL: None LANG: None LOCALE: ('English_United States', '1252') libhdf5: 1.12.1 libnetcdf: 4.8.1

xarray: 0.21.1 pandas: 1.4.0 numpy: 1.21.5 scipy: 1.8.0 netCDF4: 1.5.8 pydap: None h5netcdf: None h5py: None Nio: None zarr: 2.11.0 cftime: 1.5.2 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: 2022.01.1 distributed: 2022.01.1 matplotlib: 3.5.1 cartopy: 0.20.2 seaborn: None numbagg: None fsspec: 2022.01.0 cupy: None pint: None sparse: None setuptools: 59.8.0 pip: 22.0.3 conda: None pytest: None IPython: 8.0.1 sphinx: 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