[{"data":[{"uid":"0",/** "value": 0,*/},{"uid":"1","value":1,},{"uid":"2","value":2,}]}]

db.collection.aggregate([{"$project":{"_id":0,"value_argmax":{"$arrayElemAt":["$data.uid",{"$indexOfArray":["$data.value",{"$max":"$data.value"}]}]}}}])