[WIP] Enable save/read, simplify "combine" kwarg and allow symmetric RAM optimization

[adam2392]

PR Description

Closes: #16 Closes: #18 Closes: #10

• Reading/writing occurs as netCDF files
• Refactoring combine in the envelope_correlation function into EpochXXX
• Allow symmetric RAM optimization

Merge checklist

Maintainer, please confirm the following before merging:

• [ ] All comments resolved
• [ ] This is not your own PR
• [ ] All CIs are happy
• [ ] PR title starts with [MRG]
• [ ] whats_new.rst is updated
• [ ] PR description includes phrase "closes <#issue-number>"

[adam2392]

Looks like I'm getting hit by an error that I can't reproduce locally, but only on Ubuntu and some Mac distros:

mne_connectivity/tests/test_connectivity.py:177: in test_io
270
    conn.save(fname)
271
mne_connectivity/base.py:481: in save
272
    self.xarray.to_netcdf(fname, mode='w')
273
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/xarray/core/dataarray.py:2778: in to_netcdf
274
    return dataset.to_netcdf(*args, **kwargs)
275
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/xarray/core/dataset.py:1799: in to_netcdf
276
    return to_netcdf(
277
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/xarray/backends/api.py:1092: in to_netcdf
278
    store.close()
279
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/xarray/backends/scipy_.py:237: in close
280
    self._manager.close()
281
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/xarray/backends/file_manager.py:222: in close
282
    file.close()
283
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/scipy/io/netcdf.py:294: in close
284
    self.flush()
285
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/scipy/io/netcdf.py:404: in flush
286
    self._write()
287
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/scipy/io/netcdf.py:416: in _write
288
    self._write_var_array()
289
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/scipy/io/netcdf.py:464: in _write_var_array
290
    self._write_var_metadata(name)
291
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/scipy/io/netcdf.py:485: in _write_var_metadata
292
    self._write_att_array(var._attributes)
293
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/scipy/io/netcdf.py:445: in _write_att_array
294
    self._write_att_values(values)
295
../../../hostedtoolcache/Python/3.8.10/x64/lib/python3.8/site-packages/scipy/io/netcdf.py:557: in _write_att_values
296
    nc_type = REVERSE[values.dtype.char, values.dtype.itemsize]
297
E   KeyError: ('U', 4)

Will need to do some googling...

[adam2392]

Regarding the error: looks like the attributes are making trouble?

Ah looks like "netcdf4" library needs to be added into the requirements files :p