Get the average of an entire field using the aggregation framework in MongoDB?

You can use aggregate() method for this. Let us first create a collection with documents

> db.averageAggregationDemo.insertOne({"PlayerGameScore":45}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ed66bd628fa4220163b95") } > db.averageAggregationDemo.insertOne({"PlayerGameScore":55}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ed671d628fa4220163b96") } > db.averageAggregationDemo.insertOne({"PlayerGameScore":65}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ed676d628fa4220163b97") } > db.averageAggregationDemo.insertOne({"PlayerGameScore":35}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ed67bd628fa4220163b98") } > db.averageAggregationDemo.insertOne({"PlayerGameScore":16}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c9ed701d628fa4220163b99") }

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

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

This will produce the following output

{ "_id" : ObjectId("5c9ed66bd628fa4220163b95"), "PlayerGameScore" : 45 } { "_id" : ObjectId("5c9ed671d628fa4220163b96"), "PlayerGameScore" : 55 } { "_id" : ObjectId("5c9ed676d628fa4220163b97"), "PlayerGameScore" : 65 } { "_id" : ObjectId("5c9ed67bd628fa4220163b98"), "PlayerGameScore" : 35 } { "_id" : ObjectId("5c9ed701d628fa4220163b99"), "PlayerGameScore" : 16 } Following is the query to get the average of an entire field with aggregation: > db.averageAggregationDemo.aggregate({ "$group": { "_id": null, "PlayerGameScoreAverage": { "$avg": "$PlayerGameScore" } } } );

This will produce the following output

{ "_id" : null, "PlayerGameScoreAverage" : 43.2 }