有一个二维数组，小弟我想取出其中一个key的集合，并计算总和

array( 
        [0] => Array ( 
		[id] => 5 
		[title] => 相宜本草八倍凝水霜50g 保湿补水滋润美白面霜乳液男女正品护肤品 
		[images] => uploadfile/goods/2015-01/1420774763.jpg 
		[price] => 39.0 
		[num] => 1 
		[total] => 39 
		[wlmoney] => 0 
		[url] => http://localhost/dkyq/goods.php?id=12 ) 
		
		
        [1] => Array ( 
		[id] => 4 
		[title] => 美肤宝正品 水份源洁面膏洁面乳75ml 洗面奶清洁爽肤 补水保湿 
		[images] => uploadfile/goods/2015-01/1420773795.jpg 
		[price] => 12.0 
		[num] => 1 
		[total] => 12 
		[wlmoney] => 0 
		[url] => http://localhost/dkyq/goods.php?id=11 
		) 
);

$ar = array (
  0 => array (
    'id' => '5',
    'title' => '相宜本草八倍凝水霜50g 保湿补水滋润美白面霜乳液男女正品护肤品',
    'images' => 'uploadfile/goods/2015-01/1420774763.jpg',
    'price' => '39.0',
    'num' => '1',
    'total' => '39',
    'wlmoney' => '0',
    'url' => 'http://localhost/dkyq/goods.php?id=12',
  ),
  1 => array (
    'id' => '4',
    'title' => '美肤宝正品 水份源洁面膏洁面乳75ml 洗面奶清洁爽肤 补水保湿',
    'images' => 'uploadfile/goods/2015-01/1420773795.jpg',
    'price' => '12.0',
    'num' => '1',
    'total' => '12',
    'wlmoney' => '0',
    'url' => 'http://localhost/dkyq/goods.php?id=11',
  ),
);

$total = 0;
foreach($ar as $r) $total += $r['total'];
echo $total; //51

$arr = array(
   array(
    'id' => '5',
    'title' => '相宜本草八倍凝水霜50g 保湿补水滋润美白面霜乳液男女正品护肤品',
    'images' => 'uploadfile/goods/2015-01/1420774763.jpg',
    'price' => '39.0',
    'num' => '1',
    'total' => '39',
    'wlmoney' => '0',
    'url' => 'http://localhost/dkyq/goods.php?id=12',
  ),
  array(
    'id' => '4',
    'title' => '美肤宝正品 水份源洁面膏洁面乳75ml 洗面奶清洁爽肤 补水保湿',
    'images' => 'uploadfile/goods/2015-01/1420773795.jpg',
    'price' => '12.0',
    'num' => '1',
    'total' => '12',
    'wlmoney' => '0',
    'url' => 'http://localhost/dkyq/goods.php?id=11',
  )
);
$total = 0;
foreach($arr as $v){
    $total += $v['total'];
}
echo $total;