[Numpy-discussion] unique() should return a sorted array

Sasha ndarray at mac.com
Sun Jul 2 11:17:58 CDT 2006

On 7/2/06, Norbert Nemec <Norbert.Nemec.list at gmx.de> wrote:
> ...
> Does anybody know about the internals of the python "set"? How is
> .keys() implemented? I somehow have really doubts about the efficiency
> of this method.
Set implementation (Objects/setobject.c) is a copy and paste job from
dictobject with values removed.  As a result it is heavily optimized
for the case of string valued keys - a case that is almost irrelevant
for numpy.

I think something like the following (untested, 1d only) will probably
be much faster and sorted:

def unique(x):
      s = sort(x)
      r = empty_like(s)
      r[:-1] = s[1:]
      r[-1] = s[0]
      return s[r != s]

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