@sorted =
  map  { $_->[ 1 ] }
  sort { $a->[ 0 ] <=> $b->[ 0 ] }
  map  { [ expensivefunc( $_ ), $_ ] } @data; 

##</code><code>##

@sorted = sort { expensivefunc( $a ) <=> expensivefunc( $b ) } @data;