[{id_machine:"60ec5692a1796250f821222",time:"2021-09-10T15:24:42.365Z",value:[{cod:"CO2",val:"29"},{cod:"Temp",val:"29"},{cod:"CO2",val:"29"},{cod:"O3",val:"29"},{cod:"PM2_5_In",val:"29"},{cod:"PM2_5_Out",val:"29"},{cod:"PM10_In",val:"29"},{cod:"PM10_Out",val:"29"},{cod:"Pa1",val:"29"},{cod:"Pa2",val:"29"},{cod:"UVC",val:"29"},{cod:"Hum",val:"29"}],_id:"613b78bafd96452308232571"},{id_machine:"60ec5692a1796250f821222",time:"2021-09-10T15:25:42.365Z",value:[{cod:"CO2",val:"5"},{cod:"Temp",val:"1"},{cod:"CO2",val:"29"},{cod:"O3",val:"29"},{cod:"PM2_5_In",val:"259"},{cod:"PM2_5_Out",val:"29"},{cod:"PM10_In",val:"29"},{cod:"PM10_Out",val:"29"},{cod:"Pa1",val:"29"},{cod:"Pa2",val:"29"},{cod:"UVC",val:"22"},{cod:"Hum",val:"15"}],_id:"613b78bafd96452308232573"}]

db.collection.aggregate([{$match:{}},{$unwind:{path:"$value",}},{$group:{_id:"$value.cod",valueSum:{$sum:{"$toInt":"$value.val"}},docCount:{$sum:1}}},{$group:{_id:null,value:{$push:{cod:"$_id",avgVal:{"$divide":["$valueSum","$docCount"]}}}}}])