Jim Gibson schreef: > The problem addressed by what is know in Perl as the 'Schwartzian > Transform' is that the compare operation can be an expensive one, > regardless of the whether the comparison uses multiple keys. Since in > comparison sorts, the compare operation will be executed N(logN) > times, it is more efficient to pre-compute a set of keys, one for > each object to be sorted. That need be done only N times. The sort > can then use these pre-computed keys to sort the objects.
Basically it first builds, than sorts an index. The pre-computed (multi-)keys can often be optimized, see Uri's Sort::Maker http://search.cpan.org/search?query=Sort::Maker for facilities. -- Affijn, Ruud "Gewoon is een tijger." -- http://mail.python.org/mailman/listinfo/python-list
