You can use the following methods to count the distinct values in a specific field in MongoDB:
Method 1: Find List of Distinct Values
db.collection.distinct('field_name')
Method 2: Find Count of Distinct Values
db.collection.distinct('field_name').length
The following examples show how to use each method with a collection teams with the following documents:
db.teams.insertOne({team: "Mavs", position: "Guard", points: 31})
db.teams.insertOne({team: "Mavs", position: "Guard", points: 22})
db.teams.insertOne({team: "Rockets", position: "Center", points: 19})
db.teams.insertOne({team: "Rockets", position: "Forward", points: 26})
db.teams.insertOne({team: "Cavs", position: "Guard", points: 33})
Example 1: Find List of Distinct Values
We can use the following code to find a list of distinct values in the “team” field:
db.teams.distinct('team')
This query returns the following result:
[ 'Cavs', 'Mavs', 'Rockets' ]
The output shows the three distinct team names from all of the documents.
We could also use the following code to find a list of distinct values in the “position” field:
db.teams.distinct('position')
This query returns the following result:
[ 'Center', 'Forward', 'Guard' ]
Note: MongoDB sorts the distinct values in alphabetical order by default.
Example 2: Find Count of Unique Values
We can use the following code to count the number of distinct values in the “team” field:
db.teams.distinct('team').length
This query returns the following result:
3
This tells us that there are 3 distinct values in the “team” field.
We can also use the following code to count the number of unique values in the “points” field:
db.teams.distinct('points').length
This query returns the following result:
5
This tells us that there are 5 distinct values in the “points” field.
Note: You can find the complete documentation for the distinct function here.
Additional Resources
The following tutorials explain how to perform other common operations in MongoDB:
MongoDB: How to Group By and Count
MongoDB: How to Group By Multiple Fields
MongoDB: How to Find the Max Value in a Collection