[{"id":"1234","name":"test","elements":[{"name":"element1","type":"exaple"},{"name":"element2","type":"important"},{"name":"element3","type":"exaple"},{"name":"element4","type":"important"},{"name":"element5","type":"exaple"}]}]

db.collection.aggregate([{"$set":{"elements":{"$filter":{"input":"$elements","cond":{"$eq":["$$this.type","important"]}}}}},{"$project":{"result":"$elements.name"}}])