[{"sessionId":"f960e3db-838c-42aa-95ce-a807096f7036","date":"12-02-2020","hour":"13","month":"02","time":"13:46:50","weekDay":"Wednesday",},{"sessionId":"f960e3db-838c-42aa-95ce-a807096f7036","date":"12-02-2021","hour":"13","month":"02","time":"13:46:50","weekDay":"Wednesday",},{"sessionId":"f960e3db-838c-42aa-95ce-a807096f7036","date":"12-02-2020","hour":"12","month":"02","time":"13:46:50","weekDay":"Wednesday",},{"sessionId":"f960e3db-838c-42aa-95ce-a807096f7036","date":"12-02-2020","hour":"12","month":"02","time":"13:46:50","weekDay":"Wednesday",},{"sessionId":"f960e3db-838c-42aa-95ce-a807096f7036","date":"15-02-2020","hour":"12","month":"02","time":"13:46:50","weekDay":"Wednesday",},{"sessionId":"f960e3db-838c-42aa-95ce-a807096f7000","date":"15-02-2020","hour":"12","month":"02","time":"13:46:50","weekDay":"Wednesday",}]

db.collection.aggregate([{$group:{_id:{session:"$sessionId",date:"$date",hour:"$hour"}}},{$group:{_id:{date:"$_id.date",hour:"$_id.hour"},count:{$sum:1}}},{$project:{data:{$arrayToObject:[[{k:"$_id.date",v:{$arrayToObject:[[{k:"$_id.hour",v:"$count"}]]}}]]}}},{$replaceRoot:{newRoot:"$data"}}])