How to get max values for distinct elements in MongoDB

To get max values for distinct elements, use $sort and $group in MongoDB aggregate(). Let us create a collection with documents −

> db.demo750.insertOne({id:101,value:50});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5eae74b2a930c785c834e566")
}
> db.demo750.insertOne({id:102,value:40});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5eae74c8a930c785c834e567")
}
> db.demo750.insertOne({id:101,value:110});
{
   "acknowledged" : true,
   "insertedId" : ObjectId("5eae74dba930c785c834e568")
}

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

> db.demo750.find();

This will produce the following output −

{ "_id" : ObjectId("5eae74b2a930c785c834e566"), "id" : 101, "value" : 50 }
{ "_id" : ObjectId("5eae74c8a930c785c834e567"), "id" : 102, "value" : 40 }
{ "_id" : ObjectId("5eae74dba930c785c834e568"), "id" : 101, "value" : 110 }

Following is the query to get max values for distinct elements in MongoDB −

> db.demo750.aggregate([
...    {
...       $sort: { value: -1 }
...    },
...    {
...       $group: {
...          _id: "$id",
...          value: { $first: "$value" }
...       }
...    },
...    {
...       $project: {
...          id: "$_id",
...          value: 1
...       }
...    }
... ])

This will produce the following output −

{ "_id" : 102, "value" : 40, "id" : 102 }
{ "_id" : 101, "value" : 110, "id" : 101 }