[{"all":[{"type":"A","id":"1"},{"type":"A","id":"1"},{"type":"B","id":"2"},{"type":"A","id":"3"}]},{"all":[{"type":"A","id":"5"},{"type":"A","id":"4"},{"type":"B","id":"1"},{"type":"A","id":"11"}]}]

db.collection.aggregate([{$unwind:"$all"},{$match:{"all.type":"A"}},{$group:{_id:{"type":"$all.type","oldId":"$_id"},unique_type_A:{$addToSet:"$all.id"}}},{$project:{_id:0}}])