[{KEY_DEMOGRAPHICS:[{KEY:"MASKED_MRN.VALUE",VALUE:"1"},{KEY:"RACE.VALUE",VALUE:"WHITE"},{KEY:"ETHICITY.VALUE",VALUE:"CAUCASIAN"},{KEY:"DATE_OF_BIRTH.VALUE",VALUE:"2022-01-01"},{KEY:"SEX.VALUE",VALUE:"F"},{KEY:"MARTIAL_STATUS.VALUE",VALUE:"UNKNOWN"},{KEY:"ADDRESS1.VALUE",VALUE:"123"},]},{KEY_DEMOGRAPHICS:[{KEY:"MASKED_MRN.VALUE",VALUE:"1"},{KEY:"RACE.VALUE",VALUE:"WHITE"},{KEY:"ETHICITY.VALUE",VALUE:"CAUCASIAN"},{KEY:"DATE_OF_BIRTH.VALUE",VALUE:"2022-01-01"},{KEY:"SEX.VALUE",VALUE:"F"},{KEY:"MARTIAL_STATUS.VALUE",VALUE:"UNKNOWN"},{KEY:"ADDRESS1.VALUE",VALUE:"123"},]},{KEY_DEMOGRAPHICS:[{KEY:"MASKED_MRN.VALUE",VALUE:"3"},{KEY:"RACE.VALUE",VALUE:"BLACK"},{KEY:"ETHICITY.VALUE",VALUE:"BLACK"},{KEY:"DATE_OF_BIRTH.VALUE",VALUE:"2022-03-01"},{KEY:"SEX.VALUE",VALUE:"M"},{KEY:"MARTIAL_STATUS.VALUE",VALUE:"UNKNOWN"},{KEY:"ADDRESS1.VALUE",VALUE:"123"},]}]

db.collection.aggregate([{$unwind:"$KEY_DEMOGRAPHICS"},{$group:{_id:{key:"$KEY_DEMOGRAPHICS.KEY",value:"$KEY_DEMOGRAPHICS.VALUE"},sum:{$sum:1}}},{$group:{_id:"$_id.key",values:{$push:{k:"$_id.value",v:"$sum"}}}},{$group:{_id:null,values:{$push:{k:"$_id",v:{"$arrayToObject":"$values"}}}}},{$replaceRoot:{newRoot:{"$arrayToObject":"$values"}}}])