MongoDB average aggregation using NodeJS - node.js

Question

Good afternoon everyone.
I have an Array inside a MongoDB Document. I wan't to find a Volume inside it and make an average for whole collection on Volume parameter.
Document inside a MongoDB:
As you can see I have array inside array. I will have a lot of the same type documents and I need to make an average calculation between every document on Volumeparameter.
Problematic area of code(This is not working just showcasing my try.
function simplePipeline(db, callback) {
const collection = db.collection('ADABTC');
collection.aggregate(
[
{ '$group': { 'Volume': { '$avg': 'Array.Volume' } } }
],
function(err, cursor) {
assert.equal(err, null);
cursor.toArray(function(err, documents) {
console.log(documents)
callback(documents);
});
}
);
}
Just in case I can connect to DB username:password just for example.
How I should specify it NodeJS?
NodeJS Full Code
const MongoClient = require('mongodb').MongoClient;
const assert = require('assert');
// Connection URL
const url = 'mongodb://username:password#ip.adress.port/<dbname>?retryWrites=true&w=majority';
// Database Name
const dbName = 'Crypto';
// Create a new MongoClient
const client = new MongoClient(url, { useUnifiedTopology: true });
// Use connect method to connect to the Server
client.connect(function(err, client) {
assert.equal(null, err);
console.log("Connected correctly to server");
const db = client.db(dbName);
simplePipeline(db, function() {
client.close();
});
});
function simplePipeline(db, callback) {
const collection = db.collection('ADABTC');
collection.aggregate(
[
{ '$group': { 'Volume': { '$avg': 'Array.Volume' } } }
],
function(err, cursor) {
assert.equal(err, null);
cursor.toArray(function(err, documents) {
console.log(documents)
callback(documents);
});
}
);
}

Answer 1

Your $group syntax is just wrong:
Groups input documents by the specified _id expression and for each distinct grouping, outputs a documen
A $group stage must have a _id field specified. to group the entire collection just put any constant there.
{
'$group': {
_id: null,
'Volume': {
'$avg': '$Array.Volume'
}
}
}