有一个二维数组，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;