issues: 334154183

First github issue I've raised so apologies if it doesn't follow protocol.

I'm receiving a StopIteration: error when attempting to use the groupby function in xarray. The error only occurs when attempting to loop through a list of files - if a single file path is input, no error is generated. I've also tried using xr.open_mfdataset to open the full directory of files, but this produced the same error.

python for path in in_files: ds = xr.open_dataset(path) ds['index'] = county_mask ds = ds.set_coords('index') ds = ds.where(ds['index'].isin(cotton_county_keys)) ds.groupby('index').mean('stacked_lat_lon').to_dataframe().reset_index() Produces: ``` StopIteration Traceback (most recent call last) <ipython-input-91-f26bf31efda5> in <module>() 6 ds = ds.set_coords('index') 7 ds = ds.where(ds['index'].isin(cotton_county_keys)) ----> 8 ds.groupby('index').mean('stacked_lat_lon').to_dataframe().reset_index()

~\AppData\Local\Continuum\anaconda3\lib\site-packages\xarray\core\common.py in wrapped_func(self, dim, keep_attrs, skipna, kwargs) 52 return self.reduce(func, dim, keep_attrs, skipna=skipna, 53 numeric_only=numeric_only, allow_lazy=True, ---> 54 kwargs) 55 else: 56 def wrapped_func(self, dim=None, keep_attrs=False, **kwargs):

~\AppData\Local\Continuum\anaconda3\lib\site-packages\xarray\core\groupby.py in reduce(self, func, dim, keep_attrs, kwargs) 652 def reduce_dataset(ds): 653 return ds.reduce(func, dim, keep_attrs, kwargs) --> 654 return self.apply(reduce_dataset) 655 656 def assign(self, **kwargs):

~\AppData\Local\Continuum\anaconda3\lib\site-packages\xarray\core\groupby.py in apply(self, func, kwargs) 607 kwargs.pop('shortcut', None) # ignore shortcut if set (for now) 608 applied = (func(ds, kwargs) for ds in self._iter_grouped()) --> 609 return self._combine(applied) 610 611 def _combine(self, applied):

~\AppData\Local\Continuum\anaconda3\lib\site-packages\xarray\core\groupby.py in _combine(self, applied) 611 def _combine(self, applied): 612 """Recombine the applied objects like the original.""" --> 613 applied_example, applied = peek_at(applied) 614 coord, dim, positions = self._infer_concat_args(applied_example) 615 combined = concat(applied, dim)

~\AppData\Local\Continuum\anaconda3\lib\site-packages\xarray\core\utils.py in peek_at(iterable) 113 """ 114 gen = iter(iterable) --> 115 peek = next(gen) 116 return peek, itertools.chain([peek], gen) 117

StopIteration: As does: ds = xr.open_dataset(in_files[0]) ds['index'] = county_mask ds = ds.set_coords('index') ds = ds.where(ds['index'].isin(cotton_county_keys)) ds.groupby('index').mean('stacked_lat_lon').to_dataframe().reset_index()

However a file path works perfectly, path = r'V:\ARL\Weather\Product_Development\US_PRISM_DATA\daily_temp\PRISM_daily_temp_1993-01-08'

ds = xr.open_dataset(path) ds['index'] = county_mask ds = ds.set_coords('index') ds = ds.where(ds['index'].isin(cotton_county_keys)) ds.groupby('index').mean('stacked_lat_lon').to_dataframe().reset_index() ```