def METHOD_NAME(da):
    sos = butter(da.coords['xx'], N=4, Wn=20 / da.coords['xx'].unit)
    out2d = sosfiltfilt(da, 'xx', sos=sos)
    assert sc.identical(out2d['yy', 0], sosfiltfilt(da['yy', 0], 'xx', sos=sos))
    assert sc.identical(out2d['yy', 1], sosfiltfilt(da['yy', 1], 'xx', sos=sos))