MongoDB (PHP) - MapReduce - Connect Documents in different collections with the same ID - php

Question

I have a collection named requests with documents following this prototype:
{
"_id": {
"$id": "56295368ef2b8e5458000029"
},
"title": "Hardcoded Name",
"requestorId": "dve34gegrgeefdsfewe"
}
The requestorId of those documents correlates with the id (not the _id Mongo Object ID) of the users collection, whose documents follow this prototype:
{
"_id": {
"$id": "86235288ef2gif5458000027"
},
"id": "dve34gegrgeefdsfewe",
"name": "John Doe"
}
I need to be able to run a find() on the requests collection and obtain the name associated with the requestorId in each request document. I would normally just do the obvious: run a find() on requests, then while looping through each document, do a subsequent query on users where id = [requestorId (really "id" in users collection)], BUT I need to be able to sort the entire requests collection by the name associated with each requestorId, then use skip() & limit(). This should be pretty simple but I can't seem to figure it out... Here's my code so far, inspired by https://www.noppanit.com/merge-documents-two-collections-together-mongodb/
$m = new MongoClient(); // connect
$db = $m->{"database"};
// construct map and reduce functions
$eventRequest_map = new MongoCode("function() {
emit(this.requestorId, {\"requestorId\" : this.requestorId})
}");
$user_map = new MongoCode("function() {
emit(this.id, {\"name\" : this.name})
}");
$reductionFunction = new MongoCode("function(key, values) {
var result = {
\"requestorId\" : \"\",
\"name\" : \"\"
};
return result;
}");
$sales = $db->command(array(
'mapreduce' => "requests",
'map' => $eventRequest_map,
'reduce' => $reductionFunction,
'query' => array(),
'out' => 'joined'));
$sales = $db->command(array(
'mapreduce' => "users",
'map' => $user_map,
'reduce' => $reductionFunction,
'query' => array(),
'out' => 'joined'));
$collection = $db->joined;
$cursor = $collection->find();
$outputJoined = array();
foreach($cursor as $doc){
$outputJoined[] = $doc;
}
echo json_encode($outputJoined);