[issue11986] Min/max not symmetric in presence of NaN

[Alexander Belopolsky]

Alexander Belopolsky <belopolsky at users.sourceforge.net> added the comment:

On Sat, May 21, 2011 at 3:32 PM, Mark Dickinson <report at bugs.python.org> wrote:
..
> That might be viable (a math module function might also make sense here), though it feels a bit YAGNI to me.

I have to admit that it would be YAGNI for most of my code because it
uses numpy for numeric calculations.  Still, for consistency with
decimal, it may be a good addition.

Going a bit off-topic, I would like to mention the feature that may
actually be quite useful: float.sorting_key() that will return an
integer for each float in such a way that keys are ordered in IEEE 754
total ordering.  Note that decimal has compare_total() that can be
used for sorting, but a cmp-style method is less useful than a key
since in py3k sort does not take cmp function anymore.  Nice thing
about IEEE 754 is that  float.sorting_key()  can be implemented very
efficiently because one can simply use float's binary representation
interpreted as an integer for the key.

>  If we were going to add such a method, it should follow IEEE 754:  nan.max(x) == x.max(n) == x,
> but also nan.min(x) == x.min(nan) == x, for finite x.  (See section 5.3.1.)

Agree.  Unfortunately, numpy does not do it that way:

nan
>>> maximum(1.0, nan)
nan

I am not sure whether this is an argument for or against
float.max/min: if numpy had properly defined maximum, I would just
recommend to use that.

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