php将一维数组转换为每3个连续值组成的二维数组

<?php
$aaa = array('aa','bb','cc','dd','ee','ff','gg','hh','ii');
for($i=0;$i<3;$i++)
{
  $bbb[] = array_slice($aaa, $i * 3 ,3);
}
print_r($bbb);
?>

array
(
  [0] => array
    (
      [0] => aa
      [1] => bb
      [2] => cc
    )
  [1] => array
    (
      [0] => dd
      [1] => ee
      [2] => ff
    )
  [2] => array
    (
      [0] => gg
      [1] => hh
      [2] => ii
    )
)

$bbb[] = array_slice($aaa, $i * 3 ,3);
//3为3个一组，如果是2为2个一组