How to match and group array elements with the max value in MongoDB aggregation?

To match and group array elements with the maximum value in MongoDB aggregation, use $filter with $max to find elements with the highest score, then $group to count occurrences by name.

Syntax

db.collection.aggregate([
    {
        "$project": {
            "maxElement": {
                "$arrayElemAt": [
                    { "$filter": {
                        "input": "$arrayField",
                        "cond": { "$eq": ["$$this.score", { "$max": "$arrayField.score" }] }
                    }},
                    0
                ]
            }
        }
    },
    {
        "$group": {
            "_id": "$maxElement.name",
            "count": { "$sum": 1 }
        }
    }
])

Sample Data

db.demo510.insertMany([
    {
        "details": [
            { "Name": "Chris", "Score": 56 },
            { "Name": "David", "Score": 45 }
        ]
    },
    {
        "details": [
            { "Name": "Chris", "Score": 56 },
            { "Name": "David", "Score": 47 }
        ]
    },
    {
        "details": [
            { "Name": "Chris", "Score": 45 },
            { "Name": "David", "Score": 91 }
        ]
    }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e8845fa987b6e0e9d18f582"),
        ObjectId("5e8845fb987b6e0e9d18f583"),
        ObjectId("5e8845fb987b6e0e9d18f584")
    ]
}

Example: Find Max Score Elements and Group

db.demo510.aggregate([
    {
        "$project": {
            "details": {
                "$arrayElemAt": [
                    {
                        "$filter": {
                            "input": "$details",
                            "as": "res",
                            "cond": {
                                "$eq": [
                                    "$$res.Score",
                                    {
                                        "$max": {
                                            "$map": {
                                                "input": "$details",
                                                "as": "out",
                                                "in": "$$out.Score"
                                            }
                                        }
                                    }
                                ]
                            }
                        }
                    },
                    0
                ]
            }
        }
    },
    {
        "$group": {
            "_id": "$details.Name",
            "Name": { "$first": "$details.Name" },
            "count": { "$sum": 1 }
        }
    }
]);

{ "_id": "David", "Name": "David", "count": 1 }
{ "_id": "Chris", "Name": "Chris", "count": 2 }

How It Works

• $map extracts all Score values from the details array
• $max finds the highest score in each document's array
• $filter returns only elements matching the maximum score
• $arrayElemAt gets the first (and only) matching element
• $group counts how many times each name appears with max score

Conclusion

This aggregation pipeline efficiently identifies array elements with maximum values and groups them by name. Chris appears twice with max scores (56, 56) while David appears once with max score (91).