$ time perl  subdiscard2.pl 1000000
$VAR1 = [
          [
            '',
            '',
            9999996,
            ''
          ],
          [
            '',
            '',
            9999993,
            ''
          ],
          [
            '',
            '',
            9999990,
            ''
          ]
        ];

real    0m2.497s
user    0m2.386s
sys     0m0.108s