@sorted = map  { $_->[0] }
              sort { $a->[1] <=> $b->[1] }
              map  { [ $_, (split /[,.]/, $_)[$idx] ] } @array;

##</code><code>##

    map { chomp(my $key = (split /[,.]/, $_)[$idx]);
          [ $_, $key ] } @array;