Get MongoDB documents with max attribute per group in a collection?

To get documents with the maximum attribute per group in a MongoDB collection, use the $sort operator combined with the $group stage in an aggregation pipeline. This approach sorts documents by the grouping field and the target attribute, then uses $first to select the document with the highest value per group.

Sample Data

db.maxAttributePerGroup.insertMany([
    {
        "StudentFirstName": "John",
        "StudentLastName": "Smith",
        "StudentAge": 29,
        "StudentId": 10
    },
    {
        "StudentFirstName": "Carol",
        "StudentLastName": "Taylor",
        "StudentAge": 19,
        "StudentId": 10
    },
    {
        "StudentFirstName": "Adam",
        "StudentLastName": "Smith",
        "StudentAge": 34,
        "StudentId": 20
    },
    {
        "StudentFirstName": "Bob",
        "StudentLastName": "Taylor",
        "StudentAge": 58,
        "StudentId": 20
    }
]);

Display All Documents

db.maxAttributePerGroup.find().pretty();

{
    "_id" : ObjectId("5c76ee341e9c5dd6f1f78277"),
    "StudentFirstName" : "John",
    "StudentLastName" : "Smith",
    "StudentAge" : 29,
    "StudentId" : 10
}
{
    "_id" : ObjectId("5c76ee4e1e9c5dd6f1f78278"),
    "StudentFirstName" : "Carol",
    "StudentLastName" : "Taylor",
    "StudentAge" : 19,
    "StudentId" : 10
}
{
    "_id" : ObjectId("5c76ee631e9c5dd6f1f78279"),
    "StudentFirstName" : "Adam",
    "StudentLastName" : "Smith",
    "StudentAge" : 34,
    "StudentId" : 20
}
{
    "_id" : ObjectId("5c76ee791e9c5dd6f1f7827a"),
    "StudentFirstName" : "Bob",
    "StudentLastName" : "Taylor",
    "StudentAge" : 58,
    "StudentId" : 20
}

Get Max Attribute Per Group

This query finds the student with the maximum age in each StudentId group ?

db.maxAttributePerGroup.aggregate([
    { "$sort": { "StudentId": 1, "StudentAge": -1 } },
    { "$group": {
        "_id": "$StudentId",
        "StudentAge": { "$first": "$StudentAge" },
        "StudentFirstName": { "$first": "$StudentFirstName" },
        "StudentLastName": { "$first": "$StudentLastName" }
    }}
]);

{
    "_id" : 20,
    "StudentAge" : 58,
    "StudentFirstName" : "Bob",
    "StudentLastName" : "Taylor"
}
{
    "_id" : 10,
    "StudentAge" : 29,
    "StudentFirstName" : "John",
    "StudentLastName" : "Smith"
}

How It Works

• $sort: Orders documents by StudentId (ascending) and StudentAge (descending)
• $group: Groups by StudentId and uses $first to select the document with the highest age
• $first: Returns the first document in each group after sorting

Conclusion

Use $sort with descending order on the target attribute, then $group with $first to get documents with maximum attribute values per group. This method efficiently finds the top document in each group without complex comparisons.