[Numpy-discussion] untenable matrix behavior in SVN

Keith Goodman kwgoodman@gmail....
Tue Apr 29 13:46:41 CDT 2008

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

>  2. Would any or all of the following be just as good
>  a result?
>         a. 1d matrix
>         b. row and column vectors (1d but "oriented" for
>         linear algebra purposes)

For me, having arrays and matrices is confusing enough. Adding row and
column objects sounds even more confusing.

>  3. If 2a. and 2b. are no good for you,
>         a. would e.g. ``x[i:i+1,:]`` be too burdensome?


>         b. would ``rows`` and ``columns`` attributes that
>         yielded matrics be an offsetting convenience?

I like the idea, from earlier in the thread, of row and col being
iterators for those time when you want to work on one column or row at
a time.

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