Switch default Quantity: AttrSeries → SparseDataArray

[khaeru]

Inherited from iiasa/ixmp#191:

xarray 0.13 includes support for converting pd.DataFrame to a pydata/sparse data structure.
This should mostly obviate the need for the custom AttrSeries class.
A PR should be opened to make the change, test performance, and make any necessary adjustments.

Resources:

• Pint's technical commentary on container class hierarchy: https://pint.readthedocs.io/en/0.11/numpy.html#Technical-Commentary
• AmphoraInc/xarray_mongodb, which integrates xarray, sparse, and pint, for reference (thanks @gidden).

As of genno 1.0, all code is tested with both AttrSeries and SparseDataArray to minimize surprises on switching.

#27 should probably be done first.

[khaeru]

#27 should probably be done first.

While doing #37, it turns out that sparse.COO currently lacks some methods that xarray needs to implement its basic DataArray API. These include:

• numpy.flip, for xarray.bfill.
• numpy.nancumprod, for DataArray.cumprod.
• numpy.pad, for DataArray.shift.

These cases are now noted in the test suite, e.g.:

genno/genno/tests/core/test_quantity.py

Lines 125 to 128 in 1ad7e5b

	def test_bfill(self, tri):
	"""Test Quantity.bfill()."""
	if Quantity._get_class() is SparseDataArray:
	pytest.xfail(reason="sparse.COO.flip() not implemented")

genno is not the right place to implement them, so this issue needs to wait on those being implemented upstream.

[khaeru]

pydata/sparse#1 (comment)

[khaeru]

https://xarray.pydata.org/en/stable/user-guide/duckarrays.html gives a summary of missing operations.