Find 5 venues with the most distinct beers tutorial->beer->aggregate( [ [ '$match' => [ 'venue_name' => [ '$ne' => null ] ] ], [ '$group' => [ '_id' => [ 'venue' => '$venue_name', 'beer' => '$beer_name' ] ] ], [ '$group' => [ '_id' => '$_id.venue', count => [ '$sum' => 1 ] ] ], [ '$sort' => [ 'count' => -1 ] ], [ '$limit' => 5 ], ] ); foreach ( $res as $result ) { echo $result['_id'], ': ', $result['count'], "\n"; } ?>]]>