[{"_id":"randomString0","title":"Quality","site":{"_id":"rKFRbvH8CEbJYdzDs","title":"Title 1","addressLine1":"address1","UNID":"001","city":"cityName","createdAt":null}},{"_id":"randomString1","title":"Some2123","site":{"_id":"rKFRbvH8CEbJYdzDs","title":"Title 1","addressLine1":"address1","UNID":"001","city":"cityName","createdAt":null}},{"_id":"randomString2","title":"Random title","site":{"_id":"rKFRbvH8CEbJYdzDs","title":"Title 1","addressLine1":"address1","UNID":"001","city":"cityName","createdAt":null}},{"_id":"randomString3","title":"Another unique job","site":{"_id":"rKFRbvH8CEbJYdzDs","title":"Title 1","addressLine1":"address1","UNID":"001","city":"cityName","createdAt":null}},{"_id":"randomString4","title":"Other thing","site":{"_id":"rKFRbvH8CEbJYdzDs","title":"Title 1","addressLine1":"address1","UNID":"001","city":"cityName","createdAt":null}},{"_id":"randomString6","title":"Something else2","site":{"_id":"rKFRsssSCEbJYdzDs","title":"Title 2","addressLine1":"address2","UNID":"002","city":"cityName2","createdAt":null}},{"_id":"randomString7","title":"Something else222","site":{"_id":"rKFRsssSCEbJYdzDs","title":"Title 2","addressLine1":"address2","UNID":"002","city":"cityName2","createdAt":null}}]

db.collection.aggregate([{"$group":{"_id":"$site.UNID","myCount":{"$sum":1},"score":{"$first":"$score"}}},{"$limit":20},{"$project":{"site":"$_id","myCount":1}}])