Sum the score of duplicate column values in MongoDB documents?

To sum values of duplicate column entries in MongoDB, use the $group stage with $sum aggregation operator. This groups documents by a field and calculates the total of specified numeric fields.

Syntax

db.collection.aggregate([
    {
        $group: {
            _id: "$groupingField",
            field1Sum: { $sum: "$field1" },
            field2Sum: { $sum: "$field2" }
        }
    }
]);

Sample Data

db.demo512.insertMany([
    {"Name": "Chris", "Score1": 45, "Score2": 65, "CountryName": "US"},
    {"Name": "Chris", "Score1": 41, "Score2": 45, "CountryName": "US"},
    {"Name": "Bob", "Score1": 75, "Score2": 55, "CountryName": "US"},
    {"Name": "Bob", "Score1": 65, "Score2": 90, "CountryName": "US"}
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5e884d96987b6e0e9d18f588"),
        ObjectId("5e884da2987b6e0e9d18f589"),
        ObjectId("5e884db2987b6e0e9d18f58a"),
        ObjectId("5e884dc2987b6e0e9d18f58b")
    ]
}

Display Sample Data

db.demo512.find();

{ "_id": ObjectId("5e884d96987b6e0e9d18f588"), "Name": "Chris", "Score1": 45, "Score2": 65, "CountryName": "US" }
{ "_id": ObjectId("5e884da2987b6e0e9d18f589"), "Name": "Chris", "Score1": 41, "Score2": 45, "CountryName": "US" }
{ "_id": ObjectId("5e884db2987b6e0e9d18f58a"), "Name": "Bob", "Score1": 75, "Score2": 55, "CountryName": "US" }
{ "_id": ObjectId("5e884dc2987b6e0e9d18f58b"), "Name": "Bob", "Score1": 65, "Score2": 90, "CountryName": "US" }

Example: Sum Scores by Name

Group documents by Name and sum the Score1 and Score2 values ?

db.demo512.aggregate([
    {
        "$group": {
            "_id": "$Name",
            "Score1": { "$sum": "$Score1" },
            "Score2": { "$sum": "$Score2" },
            "CountryName": { "$first": "$CountryName" }
        }
    },
    {
        "$project": {
            "_id": 0,
            "Name": "$_id",
            "Score1": 1,
            "Score2": 1,
            "CountryName": 1
        }
    }
]);

{ "Score1": 140, "Score2": 145, "CountryName": "US", "Name": "Bob" }
{ "Score1": 86, "Score2": 110, "CountryName": "US", "Name": "Chris" }

How It Works

• $group groups documents by the Name field
• $sum calculates the total of Score1 and Score2 for each group
• $first picks the first CountryName value from each group
• $project reshapes the output to show Name instead of _id

Conclusion

Use $group with $sum to aggregate numeric values for duplicate entries. The result shows Chris's total scores (86, 110) and Bob's total scores (140, 145) from their respective duplicate documents.