How to convert an array to object in mongodb query? - mongodb

Question

I am new to mongodb and wanted to convert my array to object using pipeline. For example,
{
field1: [1,2,3,4,5],
field2: [‘a’,’b’,’c’,’d’,’e’],
}
I want the above document to be converted to,
{
fields: [
{
field1: 1,
field2: ‘a’
},
......
{
field1: 5,
field2: ‘e’
}
]
}
Any idea how I can achieve this?

Answer 1

You can use $unwind to separate your arrays.
And then format your new list with $project without forgetting to remove the duplicates created by the $unwind.
db.collection.aggregate({
"$unwind": {
path: "$field1",
includeArrayIndex: "field1_index"
}
},
{
"$unwind": {
"path": "$field2",
"includeArrayIndex": "field2_index"
}
},
{
"$project": {
"fields": {
"field1": "$field1",
"field2": "$field2"
},
"diff": {
$cmp: [
"$field1_index",
"$field2_index"
]
}
}
},
{
"$match": {
"diff": 0
}
},
{
$group: {
_id: "$_id",
fields: {
$push: "$fields"
}
}
})
Try it here

Answer 2

You can use $zip and $map and $reduce to achieve this:
db.collection.aggregate([
{
"$addFields": {
fields: {
$reduce: {
input: {
$zip: {
inputs: [
{
$map: {
input: "$field1",
as: "f1",
in: {
field1: "$$f1"
}
}
},
{
$map: {
input: "$field2",
as: "f2",
in: {
field2: "$$f2"
}
}
}
]
}
},
initialValue: [],
in: {
"$concatArrays": [
[
{
"$mergeObjects": "$$this"
}
],
"$$value"
]
}
}
}
}
}
])
MongoPlayground
Make sure both field1 and field2 are of equal length or you will lose some data.