配列の値に基づいて PHP グループ化を実装する方法

$_array = array(
    array(1,11,'2016-05-18'),
    array(2,11,'2016-05-18'),
    array(3,22,'2016-05-18'),
    array(4,22,'2016-05-18'),
    array(5,33,'2016-05-19'),
    array(6,33,'2016-05-19'),
    array(7,44,'2016-05-19'),
    array(8,44,'2016-05-19'),
    array(9,55,'2016-05-20'),
    array(10,55,'2016-05-20'),
);
var_dump(array_val_chunk($_array));
function array_val_chunk($array){
    $result = array();
    foreach ($array as $key => $value) {
      $result[$value[1].$value[2]][] = $value;
    }
    $ret = array();
    //这里把简直转成了数字的，方便同意处理
    foreach ($result as $key => $value) {
      array_push($ret, $value);
    }
    return $ret;
}

array(5) {
 [0]=>
 array(2) {
  [0]=>
  array(3) {
   [0]=>
   int(1)
   [1]=>
   int(11)
   [2]=>
   string(10) "2016-05-18"
  }
  [1]=>
  array(3) {
   [0]=>
   int(2)
   [1]=>
   int(11)
   [2]=>
   string(10) "2016-05-18"
  }
 }
 [1]=>
 array(2) {
  [0]=>
  array(3) {
   [0]=>
   int(3)
   [1]=>
   int(22)
   [2]=>
   string(10) "2016-05-18"
  }
  [1]=>
  array(3) {
   [0]=>
   int(4)
   [1]=>
   int(22)
   [2]=>
   string(10) "2016-05-18"
  }
 }
 [2]=>
 array(2) {
  [0]=>
  array(3) {
   [0]=>
   int(5)
   [1]=>
   int(33)
   [2]=>
   string(10) "2016-05-19"
  }
  [1]=>
  array(3) {
   [0]=>
   int(6)
   [1]=>
   int(33)
   [2]=>
   string(10) "2016-05-19"
  }
 }
 [3]=>
 array(2) {
  [0]=>
  array(3) {
   [0]=>
   int(7)
   [1]=>
   int(44)
   [2]=>
   string(10) "2016-05-19"
  }
  [1]=>
  array(3) {
   [0]=>
   int(8)
   [1]=>
   int(44)
   [2]=>
   string(10) "2016-05-19"
  }
 }
 [4]=>
 array(2) {
  [0]=>
  array(3) {
   [0]=>
   int(9)
   [1]=>
   int(55)
   [2]=>
   string(10) "2016-05-20"
  }
  [1]=>
  array(3) {
   [0]=>
   int(10)
   [1]=>
   int(55)
   [2]=>
   string(10) "2016-05-20"
  }
 }
}