$ time perl  subdiscard3.pl 1000000
$VAR1 = [
          [
            '',
            '',
            9999980,
            ''
          ],
          [
            '',
            '',
            9999955,
            ''
          ],
          [
            '',
            '',
            9999944,
            ''
          ]
        ];

real    0m7.605s
user    0m7.518s
sys     0m0.093s