[Numpy-discussion] max argmax combo

Charles R Harris charlesr.harris at gmail.com
Tue Sep 19 14:58:03 CDT 2006


On 9/19/06, Bill Baxter <wbaxter at gmail.com> wrote:
>
> On 9/20/06, Francesc Altet <faltet at carabos.com> wrote:
> > A Dimarts 19 Setembre 2006 19:21, Charles R Harris va escriure:
> > >
> > > Do you want both the indexes and index sorted array returned, or just
> sort
> > > the array using indexes, i.e., something like
> > >
> > > a.sort(kind="quicksort", method="indirect")
> >
> > Uh, I don't understand what do you mean by "sort the array using
> indexes",
> > sorry.
> >
>
> I think he meant do an argsort first, then use fancy indexing to get
> the sorted array.
> For a 1-d array that's just
>
>   ind = A.argsort()
>   Asorted = A[ind]
>
> That should be O(N lg N + N), aka O(N lg N)
> For A >1-d, you need an indexing expression that's a little more
> complicated, hence the discussion about making an "extract" function
> for that purpose.  Then you could say:
>
>   ind = A.argsort(axis=d)
>   Asorted = A.extract(ind,axis=d)


I'm also thinking of the name argtake.

Chuck
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