- print_r: documentation ( source)
- array_unique: documentation ( source)
<?php
$a = array();
$a[] = array('1',null);
$a[] = array('1','2');
$a[] = array('2',null);
$a[] = array('2','2');
$a[] = array('1',null);
$a[] = array('2','2');
print_r(array_unique($a));