[Numpy-discussion] untenable matrix behavior in SVN
Keith Goodman
kwgoodman@gmail....
Tue Apr 29 15:15:21 CDT 2008
On Tue, Apr 29, 2008 at 12:50 PM, Keith Goodman <kwgoodman@gmail.com> wrote:
> On Tue, Apr 29, 2008 at 11:46 AM, Keith Goodman <kwgoodman@gmail.com> wrote:
> > On Tue, Apr 29, 2008 at 11:21 AM, Alan G Isaac <aisaac@american.edu> wrote:
> > > On Tue, 29 Apr 2008, Keith Goodman apparently wrote:
> > > > I often use x[i,:] and x[:,i] where x is a matrix and i is
> > > > a scalar. I hope this continues to return a matrix.
> > >
> > > 1. Could you give an example of the circumstances of this
> > > use?
> >
> > In my use i is most commonly an array (i = M.where(y.A)[0] where y is
> > a nx1 matrix), sometimes a list, and in ipython when debugging or
> > first writing the code, a scalar. It would seem odd to me if x[i,:]
> > returned different types of objects based on the type of i:
> >
> > array index
> > idx = M.where(y.A)[0] where y is a nx1 matrix
> > x[dx,:] --> matrix
> >
> > list index
> > idx = [0]
> > x[idx,:] --> matrix?
> >
> > scalar index
> > idx = 0
> > x[idx,:] --> not matrix
>
> Here's another use case:
>
> for i in xrange(x.shape[1]):
> xi = x[:,i]
> idx = M.where(M.isfinite(xi).A)[0]
> xi = xi[idx,:]
> # more code
>
> Also the functions I have written work on matrices. If x[i,:] did not
> return a matrix, let's say it returned some other vector type object
> that you index with a scalar, then my functions will have to test
> whether the input is a full matrix or a vector since the indexing is
> different.
And here's a use case that currently doesn't work but would be nice
(for me) if it did:
x[idx,i] = M.rand(2,1)
where x is a matrix, say 4x3, idx is an array with 2 elements, and i is a scalar
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