[SciPy-User] Indexing sparse matrices with step
Pascal Lamblin
lamblinp at iro.umontreal.ca
Thu Feb 2 11:52:44 EST 2012
Hi everybody,
I've noticed that if I have a scipy.sparse matrix (csr or csc), and I
try to index into it with slices, the "step" component of my slice seems
to be silently ignored.
Is it an expected behaviour? I would have expected an error saying only
a step of None (or not providing a step at all) is supported.
Here is a small test case:
import numpy, scipy.sparse
sm = scipy.sparse.csc_matrix([[1, 0, 0], [0, 0, 0], [0, 0, 0], [0, 1, 0]])
# True, expected
numpy.all(sm[:1,:].toarray() == sm.toarray()[:1,:])
# False, expected
numpy.all(sm.toarray()[:1,:] == sm.toarray()[:1:-1,:])
# True, unexpected
numpy.all(sm[:1:-1,:].toarray() == sm[:1,:].toarray())
# False, unexpected
numpy.all(sm[:1:-1,:].toarray() == sm.toarray()[:1:-1,:])
Thanks in advance,
--
Pascal
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