Concat int array field inside an array of object into one string field in mongodb aggregate

Question

I would like to concat int array field values inside an array of objects into one string field after dividing them (by 10).

Heres the existing document format:

{ 
  "no" : "2020921008981",  
  "date" : ISODate("2020-04-01T05:19:02.263+0000"), 
  "sale" : { 
   "soldItems" : [
       {
         "itemRefId" : "5b55ac7f0550de00210a3b24", 
         "soldPrice" : NumberInt(800), 
       },
       {
         "itemRefId" : "5b55ac7f0550de00210a3b25", 
         "soldPrice" : NumberInt(1000), 
       }
     ] 
   }
 }

Expected result :

{ 
  "no" : "2020921008981",  
  "date" : ISODate("2020-04-01T05:19:02.263+0000"),  
  "priceList" : "8.0 \n 10.0"
}

The attempt with $reduce :

 priceList: {
            $reduce: {
                input: "$sale.soldItems.soldPrice",
                initialValue: "",
                in: {
                    $cond: [ { "$eq": [ { $toString: { $divide: [ "$$value", 10 ] } }, "" ] }, "$$this", { $concat: [ { $toString: { $divide: [ "$$value", 10 ] } }, "\n", "$$this" ] } ]
                }
            }
        }

But end up getting "errmsg" : "$divide only supports numeric types, not string and double" error. Any idea would be appreciated.

Answer 1

db.case.aggregate([
    {
        $set: {
            priceList: {
                $reduce: {
                    input: {
                        $map: {
                            input: "$sale.soldItems.soldPrice",
                            in: { $toString: { $divide: ["$$this", 10] } }
                        }
                    },
                    initialValue: "",
                    in: { $concat: ["$$value", "$$this", " \n "] }
                }
            }
        }
    },
    {
        $project: {
            _id: 0,
            no: 1,
            date: 1,
            priceList: 1
        }
    }
])