[Numpy-discussion] Ticket #794 and can o' worms.
Sun Jul 20 20:35:30 CDT 2008
On Sun, Jul 20, 2008 at 20:32, Charles R Harris
> On Sun, Jul 20, 2008 at 4:47 PM, Robert Kern <email@example.com> wrote:
>> On Sun, Jul 20, 2008 at 17:42, Charles R Harris
>> <firstname.lastname@example.org> 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 : a
>> > Out: array([ Inf, -Inf, NaN, 0., 3., -3.])
>> > In : sign(a).astype(int)
>> > Out:
>> > array([ 1, -1, -2147483648, 0, 1,
>> > -1])
>> > In : sign(a).astype(bool)
>> > Out: array([ True, True, True, False, True, True], dtype=bool)
>> > In : sign(a)
>> > Out: array([ 1., -1., NaN, 0., 1., -1.])
>> > In : bool(NaN)
>> > Out: 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)
> So we should shoot for:
> nan -> bool : True
> nan -> integer kind : 0
> nan -> complex : Nan+0j
> nan -> string kind : ?, currently it is any one of 'n', 'na', 'nan',
> depending on string length.
> nan -> object: float object nan.
"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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