Zip two array and create new array of object - mongodb

Question

hello all i'm working with a MongoDB database where each data row is like:
{
"_id" : ObjectId("5cf12696e81744d2dfc0000c"),
"contributor": "user1",
"title": "Title 1",
"userhasRate" : [
"51",
"52",
],
"ratings" : [
4,
3
],
}
and i need to change it to be like:
{
"_id" : ObjectId("5cf12696e81744d2dfc0000c"),
"contributor": "user1",
"title": "Title 1",
rate : [
{userhasrate: "51", value: 4},
{userhasrate: "52", value: 3},
]
}
I already try using this method,
db.getCollection('contens').aggregate([
{ '$group':{
'rates': {$push:{ value: '$ratings', user: '$userhasRate'}}
}
}
]);
and my result become like this
{
"rates" : [
{
"value" : [
5,
5,
5
],
"user" : [
"51",
"52",
"53"
]
}
]
}
Can someone help me to solve my problem,
Thank you

Answer 1

You can use $arrayToObject and $objectToArray inside $map to achieve the required output.
db.collection.aggregate([
{
"$project": {
"rate": {
"$map": {
"input": {
"$objectToArray": {
"$arrayToObject": {
"$zip": {
"inputs": [
"$userhasRate",
"$ratings"
]
}
}
}
},
"as": "el",
"in": {
"userhasRate": "$$el.k",
"value": "$$el.v"
}
}
}
}
}
])
Alternative Method
If userhasRate contains repeated values then the first solution will not work. You can use arrayElemAt and $map along with $zip if it contains repeated values.
db.collection.aggregate([
{
"$project": {
"rate": {
"$map": {
"input": {
"$zip": {
"inputs": [
"$userhasRate",
"$ratings"
]
}
},
"as": "el",
"in": {
"userhasRate": {
"$arrayElemAt": [
"$$el",
0
]
},
"value": {
"$arrayElemAt": [
"$$el",
1
]
}
}
}
}
}
}
])

Answer 2

Try below aggregate, first of all you used group without _id that grouped all the JSONs in the collection instead set it to "$_id" also you need to create 2 arrays using old data then in next project pipeline concat the arrays to get desired output:
db.getCollection('contens').aggregate([
{
$group: {
_id: "$_id",
rate1: {
$push: {
userhasrate: {
$arrayElemAt: [
"$userhasRate",
0
]
},
value: {
$arrayElemAt: [
"$ratings",
0
]
}
}
},
rate2: {
$push: {
userhasrate: {
$arrayElemAt: [
"$userhasRate",
1
]
},
value: {
$arrayElemAt: [
"$ratings",
1
]
}
}
}
}
},
{
$project: {
_id: 1,
rate: {
$concatArrays: [
"$rate1",
"$rate2"
]
}
}
}
])