my $all_val = [];
for my $aref (@$array_ref_x) {
    my $i = 0;
    for my $row (@$aref) {
        $all_val->[$i] = '' unless defined $all_val->[$i];  # for 'use warnings'
        $all_val->[$i] = $row if $row gt $all_val->[$i];
        $i++;
    }
}