MongoDB Group query to get the count of repeated marks in documents?

To get the count of repeated marks in MongoDB documents, use the $group aggregation stage with $sum to count occurrences of each unique mark value.

Syntax

db.collection.aggregate([
    {
        $group: {
            _id: "$fieldName",
            count: { $sum: 1 }
        }
    }
])

Sample Data

db.demo676.insertMany([
    {"Marks": 87},
    {"Marks": 75},
    {"Marks": 87},
    {"Marks": 65},
    {"Marks": 65}
])

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5ea41eed04263e90dac943f2"),
        ObjectId("5ea41ef304263e90dac943f3"),
        ObjectId("5ea41ef404263e90dac943f4"),
        ObjectId("5ea41ef704263e90dac943f5"),
        ObjectId("5ea41ef804263e90dac943f6")
    ]
}

Display all documents from the collection ?

db.demo676.find()

{ "_id": ObjectId("5ea41eed04263e90dac943f2"), "Marks": 87 }
{ "_id": ObjectId("5ea41ef304263e90dac943f3"), "Marks": 75 }
{ "_id": ObjectId("5ea41ef404263e90dac943f4"), "Marks": 87 }
{ "_id": ObjectId("5ea41ef704263e90dac943f5"), "Marks": 65 }
{ "_id": ObjectId("5ea41ef804263e90dac943f6"), "Marks": 65 }

Example: Count Repeated Marks

Group documents by marks and count occurrences ?

db.demo676.aggregate([
    {
        $group: {
            _id: { "Marks": "$Marks" },
            "Count": { $sum: 1 }
        }
    }
])

{ "_id": { "Marks": 75 }, "Count": 1 }
{ "_id": { "Marks": 65 }, "Count": 2 }
{ "_id": { "Marks": 87 }, "Count": 2 }

How It Works

• $group groups documents by the specified field (_id: {"Marks": "$Marks"})
• $sum: 1 adds 1 for each document in the group, effectively counting occurrences
• The result shows each unique mark value and how many times it appears

Conclusion

Use $group with $sum: 1 in MongoDB aggregation to count repeated values. This approach efficiently groups documents by field values and returns occurrence counts for analysis.