Mongodb - Array indexed by string in $addToSet operator - mongodb

Question

Suppose we have these two documents:
{
"_id" : ObjectId("5f3cdd1d0fefeba343ff3093"),
"country" : "C1",
"time" : "1994",
"value" : NumberInt(100),
"type" : "type1",
"origin" : "O1"
}
{
"_id" : ObjectId("5f3cdd1d0fefeba343ff3094"),
"country" : "C1",
"time" : "1994",
"value" : NumberInt(200),
"type" : "type1",
"origin" : "O2"
}
I want to retrieve the aggregation with the origin array indexed by strings (the value of "type"); expected output:
{
"_id" : {
"country" : "C1",
"time" : "1994"
},
"TOT" : NumberInt(300),
"count" : 2.0,
"origin" : [
"O1": NumberInt(100),
"O2": NumberInt(200)
]
}
Here we have the type of the "origin" array as {[key: string]: number}.
With the following query, the origin array is instead indexed by numbers:
use local;
db.getCollection("test_collection").aggregate(
[
{
"$match" : {
"type" : {
"$in" : [
"type1"
]
}
}
},
{
"$group" : {
"_id" : {
"country" : "$country",
"time" : "$time"
},
"TOT" : {
"$sum" : "$value"
},
"count" : {
"$sum" : 1.0
},
"origin" : {
"$addToSet" : "$value"
}
}
}
],
{
"allowDiskUse" : false
}
);

Answer 1

You can try $arrayToObject after adding in origin,
use local;
db.getCollection("test_collection").aggregate([
{ "$match": { "type": { "$in": ["type1"] } } },
{
"$group": {
"_id": {
"country": "$country",
"time": "$time"
},
"TOT": { "$sum": "$value" },
"count": { "$sum": 1.0 },
// add object like this
"origin": {
"$addToSet": {
k: "$origin",
v: "$value"
}
}
}
},
// add this
{ $addFields: { origin: { $arrayToObject: "$origin" } } }
],
{ "allowDiskUse": false }
)
Playground