Support `.squeeze()` for compatibility with `dask.array.matmul`

[Sola85]

Currently matrix-multiplication with dask arrays based on sparse arrays does not work because the .squeeze() function is not implemented:

import dask.array as da
import scipy.sparse as sp
import sparse

x_da= da.from_array(sparse.COO.from_scipy_sparse(sp.rand(2**10, 2**10)), chunks=(256, 256))
res_da = (x_da@x_da).compute()

results in

AttributeError: 'COO' object has no attribute 'squeeze'

Since reshaping is supported, I am guessing that implementing squeeze() should be fairly easy?

Versions:
sparse: 0.13.0
dask: 2022.11.1
Python 3.8.10 (default, Jun 22 2022, 20:18:18)
[GCC 9.4.0] on linux

[Hameer Abbasi]

Yes, this is a fairly easy task to do.

[Vamp]

Can someone guide me on how to contribute on this issue

[Hameer Abbasi]

@mtsokol Again, something in your wheelhouse.

[Mateusz Sokół]

@hameerabbasi Sure! We already got squeeze in #613. Let me check it with Dask example.

[Mateusz Sokół]

I checked it and with the current main branch of sparse:

x_da = da.from_array(sparse.COO.from_scipy_sparse(sp.rand(2**10, 2**10)), chunks=(256, 256))
res_da = (x_da @ x_da).compute()

correctly computes the result. So it was only COO.squeeze() that was missing.

[Hameer Abbasi]

Completed in #613.