[Numpy-discussion] Structured array copying by field name (was: Numpy 1.6 schedule)

Ralf Gommers ralf.gommers@googlemail....
Sat Mar 12 06:34:13 CST 2011


On Sat, Mar 12, 2011 at 6:51 AM, Benjamin Root <ben.root@ou.edu> wrote:
>
>
> On Fri, Mar 11, 2011 at 2:20 PM, Mark Wiebe <mwwiebe@gmail.com> wrote:
>>
>> On Fri, Mar 11, 2011 at 1:07 AM, Ralf Gommers
>> <ralf.gommers@googlemail.com> wrote:
>>>
>>> On Tue, Mar 8, 2011 at 1:35 AM, Pauli Virtanen <pav@iki.fi> wrote:
>>> >
>>> > Structured array copying copies by field name.
>>> >
>>> > Commit 22d96096bf7d5fb199ca80f2fcd04e8d27815476
>>> >
>>> > Before:
>>> >
>>> >>>> x = np.array([(0, 1)], dtype=[('a', int), ('b', int)])
>>> >>>> y = np.array([(2, 3)], dtype=[('a', int), ('b', int)])
>>> >>>> y = np.array([(2, 3)], dtype=[('b', int), ('a', int)])
>>> >>>> x[:] = y
>>> >>>> x
>>> > array([(2, 3)],
>>> >      dtype=[('a', '<i4'), ('b', '<i4')])
>>> >
>>> > After:
>>> >
>>> >>>> x = np.array([(0, 1)], dtype=[('a', int), ('b', int)])
>>> >>>> y = np.array([(2, 3)], dtype=[('b', int), ('a', int)])
>>> >>>> x[:] = y
>>> >>>> x
>>> > array([(3, 2)],
>>> >      dtype=[('a', '<i4'), ('b', '<i4')])
>>> >
>>> > This seems like a pretty hazardous change. Granted, it's in
>>> > a bit of a grey area, but people may rely on this.
>>>
>>> This is still backwards incompatible in current master. Should it be
>>> changed back for 1.6?
>>
>> I strongly dislike the behavior in 1.5 and earlier, for reasons such as
>> the example given here:
>> http://mail.scipy.org/pipermail/numpy-discussion/2011-March/055214.html
>> No problems so far have been traced back to this change, indicating that
>> this type of assignment was previously utilized very little, so I'm strongly
>> in favor of keeping it in. Based on my knowledge of the code, I'm pretty
>> sure it's a significant performance improvement as well.
>> -Mark
>
> Ditto on this.

If no problems turn up and no one objects, I am also okay with keeping
it in. Either way, I don't think this needs to be resolved before the
release of the first beta.

Cheers,
Ralf


> However, it isn't like this is fully featured anyway.
> Consider the following:
>
> x = np.array([(0, 1.1)], dtype=[('a', int), ('b', float)])
> y = np.array([(2.1, 4)], dtype=[('b', float), ('a', int)])
>
> print x + y
>
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
> TypeError: unsupported operand type(s) for +: 'numpy.ndarray' and
> 'numpy.ndarray'
>
> So, how much has people been relying on either behaviors, given that basic
> math operations weren't permissible in a similar manner?  I doubt either
> approaches would be that noticeable.
>
> Note, I would love to be able to do the above eventually.  I see a lot of
> uses for labeled arrays, especially for in the matplotlib library.  I
> personally use the larry package from time to time.
>
> Just my two cents.
> Ben Root


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