Mongodb php aggregation $match usage

gistfile1.php

$m = new MongoClient(); // connect to local mongodb
$db = $m->products; //select 'mongo database' named products
$clothing_col = $db->clothing; //create a collection from the 'table' clothing

//create the aggregation
//create the Match on clothing-category
$ops = array(
    array(
        '$match'  => array("category" => 'socks')
    )
);

$g = $clothing_col->aggregate($ops); //put the aggregation in the function

$products = $g['result']; //put results in your own var

foreach($products as $product){
  echo $product['product_name'];
}