[{"_id":{"$oid":"1201f1196affd5c74ca0af14"},"guid":"MEM-bce9","revision":121,"action":"updated"},{"_id":{"$oid":"2201f1196affd5c74ca0afc4"},"guid":"MEM-bce9","revision":122,"action":"deleted"},{"_id":{"$oid":"3201f1196affd5c74ca0afc4"},"guid":"MEM-aXt1","revision":21,"action":"created"},{"_id":{"$oid":"4201f1196affd5c74ca0afc4"},"guid":"MEM-aXt1","revision":22,"action":"updated"},{"_id":{"$oid":"5201f1196affd5c74ca0afc4"},"guid":"MEM-Mwq0","revision":121,"action":"updated"}]

db.collection.aggregate([{"$match":{}},{"$sort":{"revision":-1}},{"$group":{"_id":"$guid","latest":{"$first":"$$ROOT"}}},{"$replaceWith":"$latest"}])