Finding Nonzero Elements in a Sparse Matrix

[Robert Kern]

deLenn wrote:
> Hi,
> 
> Does scipy have an equivalent to Matlab's 'find' function, to list the
> indices of all nonzero elements in a sparse matrix?

You will want to ask scipy questions on the scipy list.

  http://www.scipy.org/Mailing_Lists

There is no explicit interface on sparse matrix objects to expose the indices of
the nonzero elements. A different implementation would have to be written for
each type of sparse matrix format. However, if one can spare the memory, one can
convert to the coordinate list format and read the row and column indices from
that object.


In [1]: from scipy.sparse import lil_matrix

In [2]: A = lil_matrix((3,3))

In [3]: A[1,2] = 10

In [4]: A[2,0] = -10

In [5]: Acoo = A.tocoo()

In [6]: Acoo.row
Out[6]: array([2, 1])

In [7]: Acoo.col
Out[7]: array([0, 2])


-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco