issue_comments: 241540585

I get the following error now when I try to run the gist code referenced in the original message above:

``` $ python -u xarray_gist.py /dev/shm/nclimgrid_prcp_reduced.nc nclimgrid_prcp_doubled.nc Traceback (most recent call last): File "xarray_gist.py", line 45, in <module> encoding = {variable_name: {'FillValue': np.nan, 'dtype': 'float32'}}) File "/home/james.adams/anaconda3/lib/python3.5/site-packages/xarray/core/dataset.py", line 782, in to_netcdf engine=engine, encoding=encoding) File "/home/james.adams/anaconda3/lib/python3.5/site-packages/xarray/backends/api.py", line 354, in to_netcdf dataset.dump_to_store(store, sync=sync, encoding=encoding) File "/home/james.adams/anaconda3/lib/python3.5/site-packages/xarray/core/dataset.py", line 728, in dump_to_store store.store(variables, attrs, check_encoding) File "/home/james.adams/anaconda3/lib/python3.5/site-packages/xarray/backends/common.py", line 234, in store check_encoding_set) File "/home/james.adams/anaconda3/lib/python3.5/site-packages/xarray/backends/common.py", line 209, in store self.set_variables(variables, check_encoding_set) File "/home/james.adams/anaconda3/lib/python3.5/site-packages/xarray/backends/common.py", line 219, in set_variables target, source = self.prepare_variable(name, v, check) File "/home/james.adams/anaconda3/lib/python3.5/site-packages/xarray/backends/netCDF4.py", line 266, in prepare_variable raise_on_invalid=check_encoding) File "/home/james.adams/anaconda3/lib/python3.5/site-packages/xarray/backends/netCDF4_.py", line 167, in _extract_nc4_encoding ' %r' % (backend, invalid)) ValueError: unexpected encoding parameters for 'netCDF4' backend: ['dtype']

```

Additionally I see the following errors when I run some other code which uses the same dataset.groupby().apply() technique (the trouble appears to show up within numpy.convolve()):

Traceback (most recent call last): File "C:\home\git\indices\src\main\python\indices\spi_gamma_xarray.py", line 46, in <module> dataset = dataset.groupby('grid_cells').apply(function_to_be_applied) File "C:\Anaconda3\lib\site-packages\xarray\core\groupby.py", line 567, in apply combined = self._concat(applied) File "C:\Anaconda3\lib\site-packages\xarray\core\groupby.py", line 572, in _concat applied_example, applied = peek_at(applied) File "C:\Anaconda3\lib\site-packages\xarray\core\utils.py", line 90, in peek_at peek = next(gen) File "C:\Anaconda3\lib\site-packages\xarray\core\groupby.py", line 566, in <genexpr> applied = (func(ds, **kwargs) for ds in self._iter_grouped()) File "C:\home\git\indices\src\main\python\indices\spi_gamma_xarray.py", line 27, in function_to_be_applied valid_max) File "C:\Anaconda3\lib\site-packages\numpy\core\numeric.py", line 1005, in convolve return multiarray.correlate(a, v[::-1], mode) TypeError: Cannot cast array data from dtype('float64') to dtype('<U32') according to the rule 'safe' Traceback (most recent call last): File "C:\home\git\indices\src\main\python\indices\spi_gamma_xarray.py", line 46, in <module> dataset = dataset.groupby('grid_cells').apply(function_to_be_applied) File "C:\Anaconda3\lib\site-packages\xarray\core\groupby.py", line 567, in apply combined = self._concat(applied) File "C:\Anaconda3\lib\site-packages\xarray\core\groupby.py", line 572, in _concat applied_example, applied = peek_at(applied) File "C:\Anaconda3\lib\site-packages\xarray\core\utils.py", line 90, in peek_at peek = next(gen) File "C:\Anaconda3\lib\site-packages\xarray\core\groupby.py", line 566, in <genexpr> applied = (func(ds, **kwargs) for ds in self._iter_grouped()) File "C:\home\git\indices\src\main\python\indices\spi_gamma_xarray.py", line 27, in function_to_be_applied valid_max) File "C:\Anaconda3\lib\site-packages\numpy\core\numeric.py", line 1005, in convolve return multiarray.correlate(a, v[::-1], mode) TypeError: Cannot cast array data from dtype('float64') to dtype('<U32') according to the rule 'safe'

Please advise if I can provide any further information which might help work this out, or if I have made wrong assumptions as to how this feature should be used. Thanks.