How to speed up $group phase in aggregation?

To speed up the $group phase, use $group along with aggregation. Let us see an example and create a collection with documents −

> db.demo423.insertOne({"Information":[101,110,87,110,98,115,101,115,89,115]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e73a60e9822da45b30346e6") }

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

> db.demo423.find();

This will produce the following output −

{ "_id" : ObjectId("5e73a60e9822da45b30346e6"), "Information" : [ 101, 110, 87, 110, 98, 115, 101, 115, 89, 115 ] }

Following is the query to speed up $group phase in aggregation −

> db.demo423.aggregate([ ...    { ...       $project: {_id: 0, 'Information': 1} ...    }, ...    { ...       $unwind: '$Information' ...    }, ...    { ...       $group:{_id: '$Information', frequency:{$sum: 1}} ...    }, ...    { ...       $sort:{frequency:-1} ...    }, ...    { ...       $limit:2 ...    } ... ])

This will produce the following output −

{ "_id" : 115, "frequency" : 3 } { "_id" : 110, "frequency" : 2 }