Database
[{"_id":"5c378eecd11e570240a9b0ac","userID":"1","isActive":"Active","areaCode":"A-1","__v":0},{"_id":"5c378eecd11e570240a9b0bb","userID":"1","isActive":"Active","areaCode":"A-2","__v":0},{"_id":"5c378eecd11e570240a9b0c5","userID":"2","isActive":"Active","areaCode":"A-1","__v":0}]
Query
db.collection.aggregate([{"$match":{"$and":[{"isActive":"Active"},{"userID":{"$exists":true}},]}},{"$group":{"_id":"$userID","areaCodes":{"$addToSet":"$areaCode"}}},{"$project":{_id:0,userID:"$_id","areaCodes":1}}])