尝试将密集和稀疏数据与scipy.spare.hstack合并时，偶尔会遇到错误：
Traceback (most recent call last):
File "hstack_error.py", line 3, in <module>
X = scipy.sparse.hstack(hstack_parts)
File "/usr/lib/python2.7/dist-packages/scipy/sparse/construct.py", line 263, in hstack
return bmat([blocks], format=format, dtype=dtype)
File "/usr/lib/python2.7/dist-packages/scipy/sparse/construct.py", line 329, in bmat
raise ValueError('blocks must have rank 2')
ValueError: blocks must have rank 2
重现此代码的最少代码是：
import scipy.sparse
hstack_parts = [[[0.17968359700312667, -0.23497267759562843, 5.5625, 12.0, 12.0, -0.3514978725245902, 4.562932312249999, 7.578125000000001, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 5.0, -1.0, -1.0, -1.0], [0.43775723232977204, -0.04553734061930783, 4.486910994764398, 12.0, 12.0, -0.33614476914571956, 2.8162986569528794, 4.74869109947644, 0.0, 0.0, 0.0, 0.0, 0.0, …