[Numpy-discussion] A question about argmax and argsort

Robert Kern robert.kern at gmail.com
Wed Dec 20 17:34:32 CST 2006

Pierre GM wrote:
> On Wednesday 20 December 2006 18:02, Tom Denniston wrote:
>> If you want the n largest item i would recommend quicksort 
> ...
>> I don't know of a way to do this in numpy.  I think it would require
>> adding a cfunction to numpy.  Perhaps an "argnth" function?
>> Does anyone else know of an existing mechanism?
> Is it really needed when you have argsort ?
>>>> x=N.array([1,3,5,2,4])
>>>> ax=N.argsort(x)
>>>> ax
> array([0, 3, 1, 4, 2])
>>>> x[ax[0]], x[ax[-1]], x[ax-3]]
> 1, 5,  3
> Or am I once again missing the point entirely ?

There are algorithms that can be faster if you can ignore the bulk of the 
irrelevant data.

Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

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