[{"_id":"abhj","id":"abhj","Main_array":[{"number":12345,"pincode":247800,"address":["vasant","vihar","kota"]}],}]

db.collection.aggregate([{$addFields:{Main_array:{"$map":{"input":"$Main_array","in":{number:"$$this.number",pincode:"$$this.pincode",addressSize:{$size:"$$this.address"}}}}}}])