[Numpy-discussion] bug in lexsort with two different dtypes?

Tom Denniston tom.denniston@alum.dartmouth....
Sat Jun 30 14:28:47 CDT 2007


thanks

On 6/30/07, Charles R Harris <charlesr.harris@gmail.com> wrote:
>
>
> On 6/26/07, Charles R Harris <charlesr.harris@gmail.com> wrote:
> >
> >
> >
> >
> > On 6/26/07, Charles R Harris < charlesr.harris@gmail.com> wrote:
> > >
> > >
> > >
> > > On 6/26/07, Tom Denniston <
> tom.denniston@alum.dartmouth.org> wrote:
> > > > In [1]: intArr1 = numpy.array([ 0, 1, 2,-2,-1, 5,-5,-5])
> > > > In [2]: intArr2 = numpy.array([1,1,1,2,2,2,3,4])
> > > > In [3]: charArr =
> numpy.array(['a','a','a','b','b','b','c','d'])
> > > >
> > > > Here I sort two int arrays.  As expected intArr2 dominates intArr1 but
> > > > the items with the same intArr2 values are sorted forwards according
> > > > to intArr1
> > > > In [6]: numpy.lexsort((intArr1, intArr2))
> > > > Out[6]: array([0, 1, 2, 3, 4, 5, 6, 7])
> > > >
> > > > This,  however, looks like a bug to me.  Here I sort an int array and
> > > > a str array.  As expected charArray dominates intArr1 but the items
> > > > with the same charArray values are sorted *backwards* according to
> > > > intArr1
> > > > In [5]: numpy.lexsort((intArr1, charArr))
> > > > Out[5]: array([2, 1, 0, 5, 4, 3, 6, 7])
> > > >
> > > > Is this a bug or am I missing something?
> > >
> >
>
>  It was a bug. It is fixed in svn.
>
> Chuck
>
> >
> >
> >
> > >
> > >
> > > Looks like a bug.
> > >
> > > In [12]: numpy.argsort([charArr], kind='m')
> > > Out[12]: array([[2, 1, 0, 5, 4, 3, 6, 7]])
> > >
> > > In [13]: numpy.argsort([intArr2], kind='m')
> > > Out[13]: array([[0, 1, 2, 3, 4, 5, 6, 7]])
> > >
> > > Both of these are stable sorts, and since the elements are in order
> should return [[0, 1, 2, 3, 4, 5, 6, 7]]. Actually, I think they should
> return [0, 1, 2, 3, 4, 5, 6, 7], I'm not sure why the returned array is 2D
> and I suspect that is a bug also. As to why the string array sorts
> incorrectly, I am not sure. It could be that the sort isn't stable, there
> could be a stride error, or the comparison is returning wrong values. My bet
> is on the first being the case.
> >
> >
> > Nevermind the 2D thingee, that was pilot error in changing lexsort to
> argsort, charArr should not be in a list:
> >
> > In [25]: numpy.argsort(charArr, kind='m', axis=0)
> > Out[25]: array([2, 1, 0, 5, 4, 3, 6, 7])
> >
> > Works just fine.
> >
> > Chuck
> >
> >
>
>
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