[SciPy-User] get best few of many: argsort( few= ) using std::partial_sort ?

denis denis-bz-gg@t-online...
Thu Jul 8 12:17:51 CDT 2010


Folks,
  to get the best few of a large number of objects,
e.g. vectors near a given one, or small distances in
spatial.distance.cdist or .pdist,
argsort( bigArray )[: a few ] is not so hot.  It would be nice if
    argsort( bigArray, few= )
did this -- faster, save mem too. Would anyone else find this useful ?

I recently stumbled across partial_sort in stl; fwiw,
std:partial_sort( A, A + sqrt(N), A + N ) is ~ 10 times faster than
std:sort
on my old mac ppc, even for N 100.
Also fwiw, nth_element alone is ~ twice as slow as partial_sort --
odd.

cheers
  -- denis


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