MongoDB Select Values above Average - mongodb

Question

I am trying to find the products whose price is above the average price.
I know how to get the average:
db.products.aggregate([{
"$group": {
"_id": null,
"average": { "$avg": "$price" }
}
},
{ $project : { _id : 0 } } ])
But how can I use it in a $gt clause?
For instance, I tried to save the result in a variable:
var averageValue =
db.products.aggregate([{
"$group": {
"_id": null,
"average": { "$avg": "$price" }
}
},
{ $project : { _id : 0 } } ])
And then use it in the $gt clause:
db.products.find({ "price": { "$gt": averageValue} })
However, it does not seem to print me anything.
I am also wondering if this is possible to be done in a single query.

Answer 1

If you use MongoDB version 5.0, you can use $setWindowFields to perform the average for all documents in the collection and add the field with result to each document.
Performs operations on a specified span of documents in a collection, known as a window, and returns the results based on the chosen window operator.
db.products.aggregate([
{
"$setWindowFields": {
"output": {
"average": {
"$avg": "$price"
}
}
}
},
{
$match: {
$expr: {
$gt: [
"$price",
"$average"
]
}
}
}
])
Sample Mongo Playground