How to select documents with values above the average in MongoDB?

MongoDBDatabaseBig Data Analytics

Use aggregate() in MongoDB to select documents with values above the average. To find the average, use $avg in MongoDB.

Let us create a collection with documents −

> db.demo552.insertOne({values:10});{
   "acknowledged" : true, "insertedId" : ObjectId("5e8e3b1c9e5f92834d7f05ea")
}
> db.demo552.insertOne({values:50});{
   "acknowledged" : true, "insertedId" : ObjectId("5e8e3b1f9e5f92834d7f05eb")
}
> db.demo552.insertOne({values:40});{
   "acknowledged" : true, "insertedId" : ObjectId("5e8e3b289e5f92834d7f05ec")
}

Display all documents from a collection with the help of find() method −

> db.demo552.find();

This will produce the following output −

{ "_id" : ObjectId("5e8e3b1c9e5f92834d7f05ea"), "values" : 10 }
{ "_id" : ObjectId("5e8e3b1f9e5f92834d7f05eb"), "values" : 50 }
{ "_id" : ObjectId("5e8e3b289e5f92834d7f05ec"), "values" : 40 }

Following is the query to select documents with values above the average −

> var findAvg = db.demo552.aggregate([
...    { "$group": { "_id": "null", Average: { "$avg": "$values"} }}
... ]).toArray()[0]["Average"];
> db.demo552.find({ "values": { "$gt": findAvg } })

This will produce the following output −

{ "_id" : ObjectId("5e8e3b1f9e5f92834d7f05eb"), "values" : 50 }
{ "_id" : ObjectId("5e8e3b289e5f92834d7f05ec"), "values" : 40 }
raja
Updated on 14-May-2020 07:56:34

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