window_correction seems sensitive to formatting of `dim`

I haven’t been able to reproduce this with synthetic data (sorry!)

But for my real data, xrft.power_spectrum(u_unfiltered.isel(x0=1000,y0=1000).load(),dim='time', window='hann',window_correction=True) gives the error:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
~/.conda/envs/pangeo2/lib/python3.7/site-packages/xarray/core/dataarray.py in _getitem_coord(self, key)
    692         try:
--> 693             var = self._coords[key]
    694         except KeyError:

KeyError: 't'

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
<ipython-input-40-09826e26c18a> in <module>
----> 1 xrft.power_spectrum(u_unfiltered.isel(x0=1000,y0=1000).load(),dim='time', window='hann',window_correction=True)

~/.conda/envs/pangeo2/lib/python3.7/site-packages/xrft/xrft.py in power_spectrum(da, dim, real_dim, scaling, window_correction, **kwargs)
    712                 )
    713             else:
--> 714                 windows, _ = _apply_window(da, dim, window_type=kwargs.get("window"))
    715                 ps = ps / (windows ** 2).mean()
    716         fs = np.prod([float(ps[d].spacing) for d in updated_dims])

~/.conda/envs/pangeo2/lib/python3.7/site-packages/xrft/xrft.py in _apply_window(da, dims, window_type)
     97             win_func(len(da[d]), sym=False), dims=da[d].dims, coords=da[d].coords
     98         )
---> 99         for d in dims
    100     ]
    101 

~/.conda/envs/pangeo2/lib/python3.7/site-packages/xrft/xrft.py in <listcomp>(.0)
     97             win_func(len(da[d]), sym=False), dims=da[d].dims, coords=da[d].coords
     98         )
---> 99         for d in dims
    100     ]
    101 

~/.conda/envs/pangeo2/lib/python3.7/site-packages/xarray/core/dataarray.py in __getitem__(self, key)
    702     def __getitem__(self, key: Any) -> "DataArray":
    703         if isinstance(key, str):
--> 704             return self._getitem_coord(key)
    705         else:
    706             # xarray-style array indexing

~/.conda/envs/pangeo2/lib/python3.7/site-packages/xarray/core/dataarray.py in _getitem_coord(self, key)
    695             dim_sizes = dict(zip(self.dims, self.shape))
    696             _, key, var = _get_virtual_variable(
--> 697                 self._coords, key, self._level_coords, dim_sizes
    698             )
    699 

~/.conda/envs/pangeo2/lib/python3.7/site-packages/xarray/core/dataset.py in _get_virtual_variable(variables, key, level_vars, dim_sizes)
    169         ref_var = dim_var.to_index_variable().get_level_variable(ref_name)
    170     else:
--> 171         ref_var = variables[ref_name]
    172 
    173     if var_name is None:

KeyError: 't'

Whereas xrft.power_spectrum(u_unfiltered.isel(x0=1000,y0=1000).load(),dim=['time'], window='hann',window_correction=True) is totally fine.

Any idea what is causing this? Is all testing performed on data with single character dimension names? Perhaps that is the problem?

[dougiesquire]

It looks like _apply_window does not support dim being a string (only a list of string). We must’ve missed this, but it should be an easy fix.

[paigem]

That would be great, thanks @dougiesquire!