[SciPy-dev] feedback on scipy.sparse

[Stefan van der Walt]

Hi Matthieu

On Wed, Dec 12, 2007 at 09:46:16AM +0100, Matthieu Brucher wrote:
>     Also, feel free to respond with any other comments related to scipy.sparse
> 
> 
> I'd like to know if some fancy indexing will be available soon. I explain
> myself. I need to populate a sparse matrix with some weights for each line. I'd
> like to do s[i, indices] = weights but it does not seem to work. I could use a
> loop, but it would be slower and this is not acceptable (as it is possible to
> do so in Matlab).

The lil_matrix is used to construct matrices like that:

In [1]: import scipy.sparse as S
In [2]: x = S.lil_matrix((3,3))

In [3]: x[0,:] = 4

In [4]: x
Out[4]: 
<3x3 sparse matrix of type '<type 'numpy.float64'>'
        with 3 stored elements in LInked List format>

In [5]: x.todense()
Out[5]: 
matrix([[ 4.,  4.,  4.],
        [ 0.,  0.,  0.],
        [ 0.,  0.,  0.]])

Regards
Stéfan