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RE: Sorting an Associative Array?

by awwaiid (Friar)
on Jul 13, 2000 at 03:15 UTC ( #22301=note: print w/replies, xml ) Need Help??


in reply to Sorting an Associative Array?

If its really big go for the Schwartzian Transform. You would end up with something like this:

@sorted = map {$_->[1]} sort { $a[0] <=> $b->[0] } map { [$_[4],$_] } @unsorted;

The second line (the "<==> part") might need to be changed if you are sorting something other than numbers. This technique is excelent for very complicated structures, very big structures, and is just neat overall :)

--awwaiid

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RE: RE: Sorting an Array?
by maverick (Curate) on Jul 13, 2000 at 18:36 UTC
    minor correction, you need a '->' in the $a in the sort:
    @sorted = map {$_->[1]} sort { $a->[0] <=> $b->[0] } map { [$_[4],$_] } @unsorted;
    and correct me if I'm mistaken (please), but isn't the Schwartzian Transform used in cases where it is necessary to modify the sort key? ie. dictonary sorting mixed case words.
    /\/\averick

      Thanks for the correction :)

      Naw, the transform doesn't have to modify the sort key... its more general purpose than that (though that is an excellent use). It is just a good algorithm for sorting (array based) data that is more complicated (and or a lot larger) than a plain array. Recently, for instance, I had an array of hashes, and used the transform to sort the array by the contents of one of the hash items.

      For instance, if we had a phone book or something, consisting of an array of hashes, each hash being an entry ($phonebook[0]{firstname} would access the firstname, for example) we could do the transform to sort by say... or something.

      @sorted_phonebook = map {$_->[1]} sort {$a->[0] cmp $b->[0]} map {[$_{lastname},$_]} @phonebook;

      Now, we could indeed do a more complex grabbing of the field we are sorting by and/or a more complex sort algorithm, one in which we needed to modify the key even, but the transform is useful for this case as well.

      --awwaiid

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