On Thu, May 20, 2010 at 10:30 AM, Ryan May <rmay31@gmail.com> wrote:
On Thu, May 20, 2010 at 9:44 AM, Benjamin Root <ben.root@ou.edu> wrote:
>> I gave two counterexamples of why.
> The examples you gave aren't counterexamples.  See below...
> On Wed, May 19, 2010 at 7:06 PM, Darren Dale <dsdale24@gmail.com> wrote:
>> On Wed, May 19, 2010 at 4:19 PM,  <josef.pktd@gmail.com> wrote:
>> > On Wed, May 19, 2010 at 4:08 PM, Darren Dale <dsdale24@gmail.com> wrote:
>> >> I have a question about creation of numpy arrays from a list of
>> >> objects, which bears on the Quantities project and also on masked
>> >> arrays:
>> >>
>> >>>>> import quantities as pq
>> >>>>> import numpy as np
>> >>>>> a, b = 2*pq.m,1*pq.s
>> >>>>> np.array([a, b])
>> >> array([ 12.,   1.])
>> >>
>> >> Why doesn't that create an object array? Similarly:
>> >>
> Consider the use case of a person creating a 1-D numpy array:
>  > np.array([12.0, 1.0])
> array([ 12.,  1.])
> How is python supposed to tell the difference between
>  > np.array([a, b])
> and
>  > np.array([12.0, 1.0])
> ?
> It can't, and there are plenty of times when one wants to explicitly
> initialize a small numpy array with a few discrete variables.

What do you mean it can't? 12.0 and 1.0 are floats, a and b are not.
While, yes, they can be coerced to floats, this is a *lossy*
transformation--it strips away information contained in the class, and
IMHO should not be the default behavior. If I want the objects, I can
force it:

In [7]: np.array([a,b],dtype=np.object)
Out[7]: array([2.0 m, 1.0 s], dtype=object)

This works fine, but feels ugly since I have to explicitly tell numpy
not to do something. It feels to me like it's violating the principle
of "in the face of ambiguity, resist the temptation to guess."

I have thought about this further, and I think I am starting to see your point (from both of you).  Here are my thoughts:

As I understand it, numpy.array() (rather, array_like()) essentially builds the dimensions of the array by first identifying if there is an iterable object, and then if the contents of the iterable is also iterable, until it reaches a non-iterable.

Therefore, the question becomes, why is numpy.array() implicitly coercing the non-iterable type into a numeric?  Is there some reason that I am not seeing for why there is an implicit coercion?

At first glance, I did not see a problem with this behavior, and I have come to expect it (hence my original reply). But now, I am not quite so sure.


Ryan May
Graduate Research Assistant
School of Meteorology
University of Oklahoma
NumPy-Discussion mailing list