[{_id:"fefesf",name:"John",info:{date:ISODate("2022-06-29T08:06:51.264Z"),marks:"12"}},{_id:"uiuioo",name:"John",info:{date:ISODate("2022-06-29T13:10:36.659Z"),marks:"15"}},{_id:"erygbo",name:"Ben",info:{date:ISODate("2022-06-29T13:10:36.659Z"),marks:"18"}}]

db.collection.aggregate([{$group:{_id:"$name",Marks:{$push:{y:"$info.marks"}}}},{$project:{Marks:{$reduce:{input:"$Marks",initialValue:[],in:{$concatArrays:["$$value",[{y:"$$this.y",x:{$add:[{$size:"$$value"},1]}}]]}}}}}])