[Matrix-SIG] min/max question and strange result

[Warren Focke]

On Wed, 13 May 1998, Konrad Hinsen wrote:

>[bsd@scripps.edu]
> > This seems odd.
> > Why is [-1] greater than [1] ??
> 
> That's a feature of Python's current comparison approach, which is
> under discussion in comp.lang.python at the moment.
> 
> Currently Python defines an order between any objects, whether that
> makes sense or not. Object types that don't define their own sense of
> order (as the numbers do) are sorted according to their memory
> address. Lists are such data types, and arrays too. That's why you get
> surprising answers.
> 
> If you want reaonsable behaviour for arrays, use NumPy functions, e.g.
> Numeric.maximum.reduce(a) to find the largest element.


NumPy does define it's own sense of order: 

>int array_compare(PyArrayObject *self, PyObject *other) {
>        /* I'd really like to raise an exception here, but I don't think
>that's possible. */
>        /* This sort of comparision doesn't make sense on arrays. */
>
>        return -1;
>}

but it's at least as surprising as comparison based on pointer value:

>>> a=array([1])
>>> b=array([1])
>>> a<b
1
>>> b<a
1

Lists define a comparison operator also, it even makes sense.


Warren Focke