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Postings from July 2003
Perhaps I am posting this to wrong list, but that has become the norm lately. :-) I noticed on this page: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/52234 titled "a guaranteed-stable sort with the decorate-sort-undecorate idiom (aka Schwartzian transform)" -------------------------------------------------------------------- "decorate-sort-undecorate" is a general and common idiom that allows very flexible and speedy sorting of Python sequences. An auxiliary list is first built (the 'decorate' step) where each item is made up of all sort-keys (in descending order of significance) of the corresponding item of the input sequence (must include all of the information in the whole corresponding item, and/or an index to it so we can fetch it back [or reconstruct it] in the third step). This is then sorted by its builtin sort method without arguments. Finally, the desired sorted-list is extracted/reconstructed by "undecorating" the now-sorted auxiliary-list. [This idiom is also known as "Schwartzian transform" by analogy with a similar Perl idiom (which, however, implies using map and grep and performing the whole sequence inside one single statement)]. -------------------------------------------------------------------- So these Python Johnnies think the Schwartzian transform uses grep, eh? I wish they gave an example. I may regret this, but I was just wondering if it would be more accurate to describe this Python decorate-sort-undecorate (DSU) thingy as a Guttman-Rosler transform? I suggest this because they state that using the builtin sort method without arguments is essential for performance reasons. My understanding is that the GR transform always uses the bald sort without arguments while the Schwartzian transform always uses a sort block. Is that right? Some links on Perl sorting: http://perlmonks.thepen.com/145659.html http://www.sysarch.com/perl/sort_paper.html /-\ http://mobile.yahoo.com.au - Yahoo! Mobile - Check & compose your email via SMS on your Telstra or Vodafone mobile.Thread Next