sub transpose {
        my $rows     = shift;
        my $max_col  = @{ $rows->[0] } - 1;
        [ map { my $c=$_; [ map {($_->[$c])} @$rows ] } 0..$max_col ]
    }

##</code><code>##

    #    [ [ 0, 1 ]     <== transpose ==>   [ [ 0, 2 ]
    #    , [ 2, 3 ] ]                       , [ 1, 3 ] ]

##</code><code>##

    my $data_by_rows = transpose(
        [ \@ns_list, \@addr_list, \@ptr_list, \@uptime_list ]
    ) ;

##</code><code>##

    $data_by_rows = [
      [
        'server1.foo-domain.net',
        '1.2.3.5',
        '5.3.2.1.in-addr.arpa',
        '131 days'
      ],
      [
        'server2.noo-domain.net',
        '11.22.33.55',
        '55.33.22.11.in-addr.arpa',
        '28 days'
      ],
      [
        'server3.zoo-domain.net',
        '22.21.20.55',
        '55.20.21.22.in-addr.arpa',
        '366 days'
      ]
    ];

##</code><code>##

    my %ns_records =
        map {( shift @$_, [ @$_ ] )} @$data_by_rows;