[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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