[Numpy-discussion] nan_to_num and bool arrays

[Robert Kern]

On Fri, Dec 11, 2009 at 16:09, Keith Goodman <kwgoodman at gmail.com> wrote:
> On Fri, Dec 11, 2009 at 1:14 PM, Robert Kern <robert.kern at gmail.com> wrote:
>> On Fri, Dec 11, 2009 at 14:41, Keith Goodman <kwgoodman at gmail.com> wrote:
>>> On Fri, Dec 11, 2009 at 12:08 PM, Bruce Southey <bsouthey at gmail.com> wrote:
>>
>>>> So I agree that it should leave the input untouched when a non-float
>>>> dtype is used for some array-like input.
>>>
>>> Would only one line need to be changed? Would changing
>>>
>>> if not issubclass(t, _nx.integer):
>>>
>>> to
>>>
>>> if not issubclass(t, _nx.integer) and not issubclass(t, _nx.bool_):
>>>
>>> do the trick?
>>
>> That still leaves strings, voids, and objects. I recommend:
>>
>>  if issubclass(t, _nx.inexact):
>>
>> Arguably, one should handle nan float objects in object arrays and
>> float columns in structured arrays, but the current code does not
>> handle either of those anyways.
>
> Without your change both
>
>>> np.nan_to_num(np.array([True, False]))
>>> np.nan_to_num([1])
>
> raise exceptions. With your change:
>
>>> np.nan_to_num(np.array([True, False]))
>   array([ True, False], dtype=bool)
>>> np.nan_to_num([1])
>   array([1])

I think this is correct, though the latter one happens by accident.
Lists don't have a .dtype attribute so obj2sctype(type([1])) is
checked and happens to be object_. The latter line is intended to
handle scalars, not sequences. I think that sequences should be
coerced to arrays for output and this check should be more explicit
about what it handles. [1.0] will have a problem if you don't.

> On a separate note, this seems a little awkward:
>
>>> np.nan_to_num(1.0)
>   1.0
>>> np.nan_to_num(1)
>   array(1)
>>> x = np.ones(1, dtype=np.int)
>>> np.nan_to_num(x[0])
>   1

Worth fixing.

-- 
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