In case you're wondering how to perform a 'distinct' query:
<?php
// Sample MongoDB command:
// db.product.distinct("scent", {"prodCat": "10 oz can"})
$manager = new MongoDB\Driver\Manager("mongodb://localhost:27017");
$query = ['prodCat' => '10 oz can']; // your typical MongoDB query
$cmd = new MongoDB\Driver\Command([
// build the 'distinct' command
'distinct' => 'product', // specify the collection name
'key' => 'scent', // specify the field for which we want to get the distinct values
'query' => $query // criteria to filter documents
]);
$cursor = $manager->executeCommand('catalog', $cmd); // retrieve the results
$scents = current($cursor->toArray())->values; // get the distinct values as an array
var_dump($scents);
?>