[PYTHON MATRIX-SIG] Final conventions for alpha2

Konrad HINSEN hinsenk@ere.umontreal.ca
Mon, 19 Aug 1996 13:14:18 -0400

> Concatenation is reasonably efficient.  It could be better, but I'm
> holding off on any non-trivial efficiency improvements until after
> release 1.0.  Right now I think a solid, stable and reasonably complete
> implementation is much more important.
> I don't see any good way to solve Carlos's problem using concatenation
> (without including arbitrary comparision functions for sort which I
> don't want to do).  How would you reccommend he gets the equivalent of:
> ix=argsort(a)
> A=take(a,ix)
> B=take(b,ix)
> for > 1d arrays without some take-like function?

Concatenation is indeed not what is needed, it is what APL
calls lamination (but it is implemented as a special case
of concatenation): the creation of a new axis along which 
the index 0 refers to a and the index 1 to b. Sort() then
reshuffles all elements automatically, and a simple indexing
recovers the sorted a and b.


Konrad Hinsen                     | E-Mail: hinsenk@ere.umontreal.ca
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