[{item:[{"_id":ObjectId("62b7c4cc2e3b0a7c3de0248f"),"adjudication":[{"amount":{"code":"USD","system":"4217","value":22.51},"category":{"coding":[{"code":"bb.org/paid_amt","system":"bb.org/adjudication"}]},"reason":{"coding":[{"code":"C","system":"bb.org/cvrg_status"}]}},{"amount":{"code":"USD","system":"4217","value":0},"category":{"coding":[{"code":"bb.org/discount_amt","system":"bb.org/adjudication"}]}}]}]}]

db.collection.aggregate([{$unwind:{path:"$item"}},{$unwind:{path:"$item.adjudication"}},{$unwind:{path:"$item.adjudication.category"}},{$unwind:{path:"$item.adjudication.category.coding"}},{$group:{_id:null,data:{$push:{k:"$item.adjudication.category.coding.code",v:"$item.adjudication.amount.value"}}}},{$project:{adjudication:{$arrayToObject:"$data"}}}])