PHP中的mongodb group操作实例(3)

> db.fruit.aggregate([ 
                     { $match: { _id: {$gt:0} } }, 
                     { $group: { _id: "$category", count: { $sum: 1 } } }, 
                     { $sort: { count: -1 } } 
                   ]); 
{ "_id" : "fruit", "count" : 3 } 
{ "_id" : "veggie", "count" : 2 } 

$cond = array( 
    array( 
        '$match' => array('_id' => array('$gt' => 0)), 
    ), 
    array( 
        '$group' => array( 
            '_id' => '$category', 
           'count' => array('$sum' => 1), 
        ), 
    ), 
    array( 
        '$sort' => array("count" => -1), 
    ), 
); 
$result = $collection->aggregate($cond); 
print_r($result);    //结果如下： 
 
Array 
( 
    [result] => Array 
        ( 
            [0] => Array 
                ( 
                    [_id] => fruit 
                    [count] => 3 
                ) 
 
            [1] => Array 
                ( 
                    [_id] => veggie 
                    [count] => 2 
                ) 
 
        ) 
 
    [ok] => 1 
)