Strange numpy.argmax behavior on object arrays in numpy 1.0.

Charles R Harris charlesr.harris at gmail.com
Sun Oct 29 18:05:37 CST 2006


On 10/29/06, Tom Denniston <tom.denniston at alum.dartmouth.org> wrote:
>
> I recently upgraded to numpy 1.0 from 1.0b5.   I noticed that numpy.argmaxbehavior is very strange on object arrays.  See below:
>
> (Pdb) numpy.__version__
> '1.0'
> (Pdb) numpy.argmax(numpy.array([2, 3], dtype=object))
> 0
> (Pdb) numpy.argmax(numpy.array([2, 3], dtype=int))
> 1
> (Pdb) numpy.argmax(numpy.array([2, 3], dtype=object), axis=0)
> 0
>
>
> I would expect the argmax to behave the same on the dtype=int and
> dtype=object examples but it doesn't.  Am I missing some subtelty or is this
> just a bug?  1.0 is the most recent version, right?
>

Suppose

In [22]: array([1,[2,3]], dtype=object)
Out[22]: array([1, [2, 3]], dtype=object)

How would you compare the elements?

In [27]: 2 < [0,0]
Out[27]: True

In [28]: [0,0] > 2
Out[28]: True

Compares memory locations?

In [28]: [2] < [0,0]
Out[28]: False

Lexical ordering?

I don't know how python interprets these things. That said, I suspect your
example should behave better, but it might give strange results sometimes
anyway.

Chuck
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