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;
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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.