[Numpy-discussion] untenable matrix behavior in SVN
Anne Archibald
peridot.faceted@gmail....
Tue Apr 29 16:03:58 CDT 2008
On 29/04/2008, Travis E. Oliphant <oliphant@enthought.com> wrote:
> I'm quite persuaded now that a[i] should return a 1-d object for
> arrays. In addition to the places Chuck identified, there are at
> least 2 other places where special code was written to work-around the
> expectation that item selection returns an object with reduced
> dimensionality (a special-cased .tolist for matrices and a special-cased
> getitem in the fancy indexing code).
>
> As the number of special-case work-arounds grows the more I'm convinced
> the conceptualization is wrong. So, I now believe we should change the
> a[i] for matrices to return a 1-d array.
>
> The only down-side I see is that a[i] != a[i,:] for matrices.
> However, matrix(a[i]) == a[i,:], and so I'm not sure there is really a
> problem, there. I also don't think that whatever problem may actually
> be buried in the fact that type(a[i]) != type(a[i,:]) is worse than the
> problem that several pieces of NumPy code actually expect hierarchical
> container behavior of multi-dimensional sequences.
I am puzzled by this. What is the rationale for x[i,:] not being a 1-d
object? Does this not require many special-case bits of code as well?
What about a[i,...]? That is what I would use to make a hierarchical
bit of code, and I would be startled to find myself in an infinite
loop waiting for the dimension to become one.
> I don't think making the small change to have a[i] return 1-d arrays
> precludes us from that 1-d array being a bit more formalized in 1.2 as a
> RowVector should we choose that direction. It does, however, fix
> several real bugs right now.
+1
What's more, I think we need to have a matrix-cleanliness test suite
that verifies that all basic numpy tools behave identically on
matrices and preserve matrixiness. But that's a big job, and for 1.2.
Anne
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