http://qs321.pair.com?node_id=9108
Description: OK - gotta add it, because I can. {grin}

For a complete description of the steps, see my column on sorting.

my @output =
  map { $_->[0] }
  sort { $a->[1] cmp $b->[1] }
  map { [$_, expensive_func($_)] }
  @input;