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

On Sun, Jul 20, 2008 at 4:47 PM, Robert Kern wrote:

On Sun, Jul 20, 2008 at 17:42, Charles R Harris wrote:

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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.

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

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

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int(nan) 0L

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. Chuck