Calculating average value per document with sort in MongoDB?

To calculate average, use aggregate along with $avg. Let us first create a collection with documents −

> db.calculateAverage.insertOne({'Value':[10,20,80]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e0383e3f5e889d7a51994dc")
}
> db.calculateAverage.insertOne({'Value':[12,15,16]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e0383edf5e889d7a51994dd")
}
> db.calculateAverage.insertOne({'Value':[30,35,40]});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5e0383f5f5e889d7a51994de")
}

Following is the query to display all documents from a collection with the help of find() method −

> db.calculateAverage.find().pretty();

This will produce the following output −

{
   "_id" : ObjectId("5e0383e3f5e889d7a51994dc"),
   "Value" : [
      10,
      20,
      80
   ]
}
{
   "_id" : ObjectId("5e0383edf5e889d7a51994dd"),
   "Value" : [
      12,
      15,
      16
   ]
}
{
   "_id" : ObjectId("5e0383f5f5e889d7a51994de"),
   "Value" : [
      30,
      35,
      40
   ]
}

Following is the query to calculate average value per document with sort −

> db.calculateAverage.aggregate([ { "$addFields": { "calavg": { "$avg": "$Value" } }}, { "$sort": { "calavg": 1 } } ],function(err, out) { res.send(out) });

This will produce the following output −

{ "_id" : ObjectId("5e0383edf5e889d7a51994dd"), "Value" : [ 12, 15, 16 ], "calavg" : 14.333333333333334 }
{ "_id" : ObjectId("5e0383f5f5e889d7a51994de"), "Value" : [ 30, 35, 40 ], "calavg" : 35 }
{ "_id" : ObjectId("5e0383e3f5e889d7a51994dc"), "Value" : [ 10, 20, 80 ], "calavg" : 36.666666666666664 }