[{"compId":"607019361c071256e4f0d0d5","courseId":"608952e3abebbd503ba6e115","playerId":"609d0993906429612483cea0","holes":{"1":2,"2":1,"3":2,"4":2,"5":2,"6":2,"7":0,"8":2,"9":3},"playerName":"Tiger Woods","total":16}]

db.collection.aggregate([{"$group":{_id:"$playerName",total:{$sum:"$total"},rounds:{$push:{k:"$courseId",v:"$holes"}}}},{$addFields:{rounds:{"$arrayToObject":"$rounds"}}}])