Database
[{"caseNumber":"2020921008981","startTime":ISODate("2016-05-18T16:00:00Z"),"salesOrder":{"purchaseItems":[{"itemRefId":"5b55ac7f0550de00210a3b24","soldPrice":800,},{"itemRefId":"5b55ac7f0550de00210a3b25","soldPrice":1000,}]}}]
Query
db.collection.aggregate([{$addFields:{"itemPriceList":{$rtrim:{input:{$reduce:{input:"$salesOrder.purchaseItems",initialValue:"",in:{$concat:["$$value",{$toString:{$divide:["$$this.soldPrice",10]}},"\n"]}}},chars:"\n"}}}}])