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

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
}
}
])

Answer 2

Try the following aggregation query, where the idea is to:
First divide the field soldPrice by 10 or required divisor using $divide
Convert it into string and concat using $toString and $concat
the appender \n gets appended after each reduce op,remove that from the end using $rtrim
create the new field using $addFields
Query:
db.collection.aggregate([
{
$addFields: {
"itemPriceList": {
$rtrim: {
input: {
$reduce: {
input: "$salesOrder.purchaseItems",
initialValue: "",
in: {
$concat: [
"$$value",
{
$toString: {
$divide: [
"$$this.soldPrice",
10
]
}
},
"\n"
]
}
}
},
chars: "\n"
}
}
}
}
]);
Result:
[
{
"_id": ObjectId("5a934e000102030405000000"),
"caseNumber": "2020921008981",
"itemPriceList": "80\n100",
"salesOrder": {
"purchaseItems": [
{
"itemRefId": "5b55ac7f0550de00210a3b24",
"soldPrice": 800
},
{
"itemRefId": "5b55ac7f0550de00210a3b25",
"soldPrice": 1000
}
]
},
"startTime": ISODate("2016-05-18T16:00:00Z")
}
]
Plaground Test Link