3v4l.org

run code in 300+ PHP versions simultaneously
<?php $array = array ( 'parent_id' => array ( 9 => array ( 0 => 11, 1 => 12 ), 10 => array ( 0 => 13, 1 => 14 ), 20 => array ( 0 => 21, 1 => 22 ), 21 => array ( 0 => 23 ) ) ); // re-index to 0 $array = array_values($array['parent_id']); // output array $pairs = array(); for ($i = 0; $i < count($array) - 1; $i += 2) { for ($j = 0; $j < min(count($array[$i]), count($array[$i+1])); $j++) { $pairs[] = array($array[$i][$j], $array[$i+1][$j]); } } print_r($pairs);
Output for 7.1.25 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.26, 8.4.1 - 8.4.13
Array ( [0] => Array ( [0] => 11 [1] => 13 ) [1] => Array ( [0] => 12 [1] => 14 ) [2] => Array ( [0] => 21 [1] => 23 ) )

preferences:
111.7 ms | 408 KiB | 5 Q