How do you get the middle result from a mongodb query - mongodb

Question

I have a MongoDB database, which has a collection that contains all of the addresses from a country. Sometimes when I execute a query on that I have a chance that I receive about 200 results (house numbers within that street). I want to get the middle item of that result.
When I do that in my coding like this for example:
const result = Address.find({ street: "fooStreet" })
// results in an array with a length of let's say 200 (could also be 20, 49, 103, etc) items
I could split it in my coding like below:
const middleIndex = Math.round(result.length / 2);
const house = result[middleIndex];
But this means that the other records go to waste and use unnecessary bandwidth + computing power which should be handled by the database. Since the database OS is optimized for working with collections etc, I was wondering if I could achieve the same result in a mongodb query? See pseudo below:
db.getCollection("addresses")
.find({ street: "fooStreet" })
.helpMeHere()
// ^ do something to get the middle result from the N items

Answer 1

You can do as below
db.collection.aggregate([
{ //Any match condition
$match: {}
},
{
$group: {//get the total matching result
"_id": null,
data: {
$push: "$$ROOT"
},
count: {
$sum: 0.5
}
}
},
{
$project: {//get the second half
"result": {
"$slice": [
"$data",
{
"$toInt": {
"$multiply": [//Negating results records from the last
{
"$toInt": "$count"
},
-1
]
}
}
]
}
}
}
])
playground
To get one element:
playground
db.collection.aggregate([
{
$match: {}
},
{
$group: {
"_id": null,
data: {
$push: "$$ROOT"
},
count: {
$sum: 0.5
}
}
},
{
$project: {
"result": {
"$arrayElemAt": [//array access
"$data",
{
"$toInt": "$count"
}
]
}
}
}
])