Php basic questions: two-dimensional array summation

Php basic question: two-dimensional array summation! Array: $ a & nbsp; array (a & gt; aa, a1 & gt; 1, a2 & gt; 1), array (a & gt; bb, a1 & gt; 2, a2 & gt; 2), array (a & gt; cc, a1 & gt; 3, a2 & gt; 3 ), array (a & g php basic question two-dimensional array summation!
Array:
$ A = array ("a" => "aa", "a1" => 1, "a2" => 1 ), array ("a" => "bb", "a1" => 2, "a2" => 2), array ("a" => "cc ", "a1" => 3, "a2" => 3), array ("a" => "aa", "a1" => 1, "a2" => 1), array ("a" => "bb", "a1" => 5, "a2" => 5 ))
Sum of elements with the same key value
Result
$ R = array ("a" => "aa", "a1" => 2, "a2" => 2 ), array ("a" => "bb", "a1" => 7, "a2" => 7), array ("a" => "cc ", "a1" => 3, "a2" => 3 ));
------ Solution --------------------

$a = array(
  array("a" => "aa", "a1" => 1, "a2" => 1),
  array("a" => "bb", "a1" => 2, "a2" => 2),
  array("a" => "cc", "a1" => 3, "a2" => 3),
  array("a" => "aa", "a1" => 1, "a2" => 1),
  array("a" => "bb", "a1" => 5, "a2" => 5),
);
$res = array();
foreach($a as $r) {
  if(! isset($res[$r['a']])) $res[$r['a']] = $r;
  else {
    $res[$r['a']]['a1'] += $r['a1'];
    $res[$r['a']]['a2'] += $r['a2'];
  }
}
print_r(array_values($res));

Array
(
    [0] => Array
        (
            [a] => aa
            [a1] => 2
            [a2] => 2
        )

    [1] => Array
        (
            [a] => bb
            [a1] => 7
            [a2] => 7
        )

    [2] => Array
        (
            [a] => cc
            [a1] => 3
            [a2] => 3
        )

)