[SciPy-user] sparse+slice? (and hello!)

[Ed Schofield]

On 17/05/2006, at 9:19 AM, Bram de Jong - MTG wrote:

> Hello everyone,
>
> ( First post on this list... Using SciPy in various algorithms and
> extensions, all related to audio processing )
>
> * A simple question to start of with, is it correct to say that the
> sparse matrices do not support slicing?
>
>> values = [0.1, 5.8, 21.8]
>> indices = [[0,0],[1,1],[2,1]]
>> matrix = sparse.coo_matrix(values, indices, 3, 3)
>> matrix = matrix.tocsc()
>> matrix2[1,1]
> 5.7999999999999998
>> matrix2[1,:]
> Traceback (most recent call last):
>    File "<input>", line 1, in ?
>    File "C:\PYTHON23\lib\site-packages\scipy\sparse\Sparse.py", line
> 578, in __getitem__
>      raise KeyError, "Index out of bounds."
> KeyError: 'Index out of bounds.'
>
> This using the scipy from the latest 'enthought' python installer for
> windows.

I've added some support for slicing in more recent SVN versions.   
It's now possible to use csc[:, j], csr[i, :], or lil[i, :].  These  
should be efficient operations.  But slicing along the 'non-native'  
axes, with csc[i, :], csr[:, j], or lil[:, j] would be slower (and  
more complex to write), and these raise an IndexError.

> * a not-so-simple question: is there any documentation, tutorial,
> introduction, ... to the sparse matrices of scipy? It seems neither  
> the
> official (feebased) docs mention them, nor are the docstrings *that*
> extensive.

There are also more docstrings in SVN HEAD.  No tutorial yet,  
although we've had several requests recently.  I'll see what I can do  
after I've submitted my thesis in a few weeks ...

-- Ed