[{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"}]

db.collection.aggregate([{$unwind:{path:"$value",}},{$group:{_id:{"$concat":["$id_machine","$time","$value.cod"]},Avg_val:{$avg:{$toInt:"$value.val"}},cod:{$first:"$value.cod"},id_machine:{$first:"$id_machine"},time:{"$first":"$time"}}}])