[Numpy-discussion] Ticket #794 and can o' worms.

Robert Kern robert.kern@gmail....
Sun Jul 20 17:47:18 CDT 2008


On Sun, Jul 20, 2008 at 17:42, Charles R Harris
<charlesr.harris@gmail.com> wrote:
> Hi All,
>
> I "fixed" ticket #754, but it leads to a ton of problems. The original
> discussion is here. The problems that arise come from conversion to
> different types.
>
> In [26]: a
> Out[26]: array([ Inf, -Inf,  NaN,   0.,   3.,  -3.])
>
> In [27]: sign(a).astype(int)
> Out[27]:
> array([          1,          -1, -2147483648,           0,           1,
>                 -1])
>
> In [28]: sign(a).astype(bool)
> Out[28]: array([ True,  True,  True, False,  True,  True], dtype=bool)
>
> In [29]: sign(a)
> Out[29]: array([  1.,  -1.,  NaN,   0.,   1.,  -1.])
>
> In [30]: bool(NaN)
> Out[30]: True
>
> So there are problems with at minimum the following.
>
> 1) The way NaN is converted to bool. I think it should be False.

It's not really our choice. That's Python's bool(). For the things
that are our choice (e.g. array([nan]).astype(bool)) I think we should
stay consistent with Python.

> 2) The way NaN is converted to int types. I think it should be 0.

I agree. That's what int(nan) gives:

>>> int(nan)
0L

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
 -- Umberto Eco


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