[SciPy-user] csr_matrix

Sam frizou excellent.frizou at gmail.com
Wed Nov 1 05:13:36 CST 2006


Thanks a lot.

I have another problem with sparse matrices please. I do not find how
to apply an operation directly to an entire row. For example,
m[1,:]=dot(m[1,:],4) does not work and I didnt found a "setrow" method
in the documentation.

Thanks



On 11/1/06, Robert Cimrman <cimrman3 at ntc.zcu.cz> wrote:
> Sam frizou wrote:
> > Hi,
> >
> > Is it possible to get the set of indices of non null elements of a
> > sparse matrix M ?
> > I means I can see them by doing "print M", but I want to use them, so
> > I would like something like a list of (i,j).
>
> A general way (should work for any kind of sparse matrix) is:
> [M.rowcol(ii) for ii in xrange(M.size)].
>
> for csr_matrix, you can use directly M.colind (array of all column
> indices), M.indptr (array pointing to first index of a row in colind)
> attributes, but I would not recommend it, unless the first approach is
> too slow.
>
> cheers,
> r.
>
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