PHP basics related issues: summation of two-dimensional arrays_PHP tutorial

PHP basic problem of summing two-dimensional arrays!

Array:

　$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))

Sum the first element with the same key value

Results

　$r = array(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

　)

　)