MongoDB - Way to find closest results from arrays inside every document - mongodb

Question

I want to find closest result from array inside document for every doc, and project it new object using MongoDB. It will be easier to explain what I trying to do by example:
Doc schema:
{
"id": "string",
"name": "string",
"track" : [
{
"time": "number",
"distance": "number"
}
]
}
EXAMPLE:
I want to find closest results for every doc for time equals 4
Input data:
[
{
"id": "1",
"name": "test1",
"track" : [
{
"time": 0,
"distance": 0
},
{
"time": 1,
"distance": 5
},
{
"time": 3,
"distance": 17
},
{
"time": 4,
"distance": 23
},
{
"time": 6,
"distance": 33
}
]
},
{
"id": "2",
"name": "test2",
"track" : [
{
"time": 0,
"distance": 0
},
{
"time": 1,
"distance": 5
},
{
"time": 2,
"distance": 12
},
{
"time": 4,
"distance": 26
},
{
"time": 6,
"distance": 32
}
]
},
{
"id": "3",
"name": "test3",
"track" : [
{
"time": 0,
"distance": 0
},
{
"time": 1,
"distance": 5
},
{
"time": 3,
"distance": 12
}
]
}
]
Output data:
[
{
"id": "1",
"result" : {
"time": 4,
"distance": 23
}
},
{
"id": "2",
"result" : {
"time": 4,
"distance": 26
}
},
{
"id": "3",
"result" : {
"time": 3,
"distance": 12
}
}
]
Is it possible to do this using MongoDB?

Answer 1

db.collection.aggregate([
{
"$addFields": {
"tracks": {
"$filter": {
"input": "$track",
"as": "track",
"cond": {
"$lte": [
"$$track.time",
4
]
}
}
}
}
},
{
"$addFields": {
"tracks": {
"$slice": [
"$tracks",
-1
]
}
}
},
{
"$unwind": "$tracks"
},
{
"$project": {
"tracks": 1,
"name": 1
}
}
])
Play
It does below things:
Finds whose track time is <=4 and adds it to an array called items
Then it gets the last element - i.e closer element
Take the element from array - unwind
Projects what is needed.