PHP让数组中有相同值的组成新的数组

$arr = array(    0=>array('key1'=>'value1' , 'key2'=>'value2'),    1=>array('key1'=>'value1' , 'key2'=>'value3'),    2=>array('key1'=>'value2' , 'key2'=>'value4'),    999=>array('key1'=>'value2' , 'key2'=>'value5'));$result = array();foreach ($arr as $data) {    isset($result[$data['key1']]) || $result[$data['key1']] = array();    $result[$data['key1']][] = $data['key2'];}ksort($cityAr, SORT_NATURAL);//这个是键值按字母先后顺序排列print_r($result);//输出如下Array(    [value1] => Array        (            [0] => value2            [1] => value3        )    [value2] => Array        (            [0] => value4            [1] => value5        )        )