CODEWITHSUNDEEP
mongodb
Leslie Optional
Leslie Optional

Reputation: 178

How can I get a list of unique values for the same field in mongo?

I have a data set like this

     {name: john,
      age:20,
      ....
      }
     {name: sally,
      age: 40
      ...
      }
     {name: sally,
      age: 50
      ...
      }

What mongo query could I issue to get back every unique value for "name". So simply it would return 'john' and 'sally'

Upvotes: 2

Views: 2542

Answers (1)

chridam
chridam

Reputation: 103445

The easiest way to get every unique value for "name" is by using the distinct() method on the collection which will query the distinct values for a specified field across a single collection and returns the results in an array. Thus use it as

var distinctNames = db.collection.distinct("name");
printjson(distinctNames);

Sample Output:

[ "sally", "john" ]

Then another way, though not as simple and straightforward as the above, is to use the aggregation framework where you use the $group pipeline stage to group the documents by the name key and outputs to the next stage a document for each distinct grouping.

With the cursor returned from the aggregate() method, you can then use its map() method to create the desired final array. The following mongo shell demonstration describes the above concept:

var distinctNames = db.collection.aggregate([
    {
        "$group": {
            "_id": "$name"
        }
    }
]).map(function (r){ return r._id; });
printjson(distinctNames);

Sample Output:

[ "sally", "john" ]

Upvotes: 2

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