[Numpy-discussion] .T Transpose shortcut for arrays again

Sasha ndarray at mac.com
Thu Jul 6 11:21:43 CDT 2006


I would like to raise a few objections going from mild to strong:

1. .T : I am mildly against it.  As an inexpensive operation that
returns a view (so that a.T[...] = makes sense) it is a reasonable
candidate for an attribute.  Unfortunately reversing the order of axes
at least as reasonable as swapaxes(-2,-1) and swapaxes(-2,-1) is
invalid for rank < 2.  My main objection is that a.T is fairly cryptic
- is there any other language that uses attribute for transpose?
Adding .T to arrays will lead to less readable code because in
expressions like "a * b.T" it will not be clear whether * is a matrix
or elemenwise multiplication.

2. .H :  This is an  O(n^2) complexity operation returning a copy so
it is not appropriate for an attribute.  It does not make much sense
for any type other than complex, so it's use is limited.

3. .M : I am strongly against this. It will create a circular
dependency between ndarray and matrix.  I would expect that asmatrix
is mostly used to convert function arguments and for this purpose
@matrix_args decorator would be a better solution to reduce code
clutter.

4. .A : I have no clue what this one does, so I won't comment.

On 7/6/06, Travis Oliphant <oliphant.travis at ieee.org> wrote:
> Bill Baxter wrote:
> > So in short my proposal is to:
> > --  make a.T a property of array that returns a.swapaxes(-2,-1),
> > --  make a.H a property of array that returns
> > a.conjugate().swapaxes(-2,-1)
> > and maybe
> > --  make a.M a property of array that returns numpy.asmatrix(a)
>
> I've tentatively implemented all of these suggestions as well as adding
> the .A attribute to the ndarray as well (so that all sub-classes and
> array scalars can get back a view as an ndarray).
>
> I did this to make it easier to do matrix-like calculations with or
> with-out matrices.   Matrix-calculation flexibility is still a sore-spot
> for many and I think these syntatical-sugar attributes will help long term.
>
> If there are no strong objections, then the recent  MATH attribute
> checkin will stay.  If there are major objections, then we can back them
> out without too much trouble as well.
>
> -Travis
>
>
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