[{"_id":"6048b2b190422d0066d90740","Code":"A0ABI61YH","Amount":100},{"_id":"6048b3cc7e4b350072424f4c","Code":"A0ABEAXX6","Amount":100},{"_id":"6048b5167e4b350072424f50","Code":"A0ABCENPD","Amount":100}]

db.collection.aggregate([{$group:{_id:null,result:{$push:{_id:"$_id",Amount:"$Amount"}}}},{$project:{_id:0,result:{$reduce:{input:"$result",initialValue:{Amount:0,_ids:[]},in:{$cond:[{$lt:["$$value.Amount",180]},{_ids:{$concatArrays:["$$value._ids",["$$this._id"]]},Amount:{$sum:["$$value.Amount","$$this.Amount"]}},"$$value"]}}}}}])