# [SciPy-User] How to get the index iterator of a scipy sparse matrix?

Warren Weckesser warren.weckesser@enthought....
Mon Mar 26 17:25:39 CDT 2012

```On Sun, Mar 25, 2012 at 5:47 PM, Pengkui Luo <pengkui.luo@gmail.com> wrote:

> e.g. suppose A is a scipy lil sparse matrix, and the result of print(A) is:
>
>   (0, 1) 1.0
>   (0, 2) -1.0
>   (1, 0) 1.0
>   (1, 2) -1.0
>   (2, 1) 2.0
>
> How can I get an iterator (or at least a list) of these (i, j) index pairs?
>
> Thanks!
>
>

You could convert the matrix to DOK format and get the keys:

In [1]: from scipy.sparse import lil_matrix

In [2]: a = lil_matrix([[0,0,0],[0,10,0],[20,0,30]])

In [3]: a.todok().keys()
Out[3]: [(2, 0), (1, 1), (2, 2)]

In [4]: a.todense()
Out[4]:
matrix([[ 0,  0,  0],
[ 0, 10,  0],
[20,  0, 30]])

That is not the most efficient method, but it is certainly easy to
implement.

Warren
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