[SciPy-dev] Scipy equivalents of MATLAB's sparse/find/accumarray
Mon Apr 7 15:39:25 CDT 2008
On Mon, Apr 7, 2008 at 1:53 PM, Viral Shah
> Nathan, thanks for your earlier response on sparse matrix indexing.
> The other thing that I found cumbersome with the current sparse
> implementation in scipy is not being able to figure out the exact
> equivalents of Matlab's sparse/accumarray and find. In the following
> examples, I will denote Matlab codes with M>> and Python with P>>
> M>> S = sparse (I, J, V, m, n)
> The equivalent in Python seems to be:
> P>> S = sparse.csc_matrix ((obj, ij), dims)
> P>> S = sparse.csr_matrix ((obj, ij), dims)
That's correct. These are just wrappers for
coo_matrix((obj,ij)).tocsc() and coo_matrix((obj,ij)).tocsr().
Likewise, find() in MATLAB implemented by .tocoo().
> It wasn't clear looking at the documentation, what happens when there
> are duplicate row/col values. Matlab's sparse() adds duplicates, and
> accumarray() provides a more general way to combine duplicates. I was
> wondering, if it would be possible to add an extra argument that would
> allow the user to specify what to do with duplicates. Options could be
> last, any, sum, prod, max, min, argmax, argmin, or a user specified
Currently the coo->csr and coo->csc conversions sum duplicates together.
accumarray() is probably better accomplished by argsorting the index
tuples and performing whatever transformation you wish on the permuted
Nathan Bell firstname.lastname@example.org
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