[Numpy-discussion] Sign of NaN

[Charles R Harris]

On Tue, Sep 29, 2015 at 7:31 PM, Charles R Harris <charlesr.harris at gmail.com
> wrote:

>
>
> On Tue, Sep 29, 2015 at 6:58 PM, Chris Barker - NOAA Federal <
> chris.barker at noaa.gov> wrote:
>
>>
>> One of the usecases that has sneaked in during the last few numpy
>> versions is that object arrays contain numerical arrays where the shapes
>> don't add up to a rectangular array.
>>
>>
>> I think that's the wrong way to dve that problem -- we really should have
>> a "proper" ragged array implementation. But is is the easiest way at this
>> point.
>>
>> For this, and other use-cases, special casing Numpy arrays stored in
>> object arrays does make sense:
>>
>> "If this is s a Numpy array, pass the operation through."
>>
>
> Because we now (development) use rich compare, the result looks like
>
> In [1]: a = ones(3)
>
> In [2]: b = array([a, -a], object)
>
> In [3]: b
> Out[3]:
> array([[1.0, 1.0, 1.0],
>        [-1.0, -1.0, -1.0]], dtype=object)
>
> In [4]: sign(b)
> Out[4]:
> array([[1L, 1L, 1L],
>        [-1L, -1L, -1L]], dtype=object)
>
> The function returns long integers in order to not special case Python 3.
> Hmm, wonder if we might want to change that.
>

Oops, not what was intended. In fact it raises an error

In [7]: b
Out[7]: array([array([ 1.,  1.,  1.]), array([-1., -1., -1.])],
dtype=object)

In [8]: sign(b)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-8-3b1a81271d2e> in <module>()
----> 1 sign(b)

ValueError: The truth value of an array with more than one element is
ambiguous. Use a.any() or a.all()

Chuck



>
> Chuck
>
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