[{value1:"same",value2:"unique"},{value1:"same",value2:"unique1"},{value3:"new"}]

db.collection.aggregate([{"$project":{kv:{"$objectToArray":"$$ROOT"}}},{"$unwind":"$kv"},{"$match":{"kv.k":{$ne:"_id"}}},{$group:{_id:{k:"$kv.k",v:"$kv.v"},cnt:{$sum:1}}}])