[PERL] 행열을 모두 열로 변환시킬때 문제

#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;
 
my $matrix = [ [undef, 1, 2, 3],
               [undef, 4, 5, 6],
               [undef, 7, 8, 9] ];
 
my $new_matrix = [];
 
foreach my $row (@$matrix) {
    push $new_matrix, map { [ $row->[$_] ] } 1 .. $#{$row};
}
 
print Dumper($new_matrix);

$VAR1 = [
          [ 1 ],
          [ 2 ],
          [ 3 ],
          [ 4 ],
          [ 5 ],
          [ 6 ],
          [ 7 ],
          [ 8 ],
          [ 9 ]
        ];