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Retrieve Distinct Values

On this page

  • Overview
  • Sample Documents
  • Distinct
  • Document Field Parameter
  • Example
  • Query Parameter
  • Options Parameter
  • Additional Information
  • API Documentation

Overview

Use the distinct() method to retrieve all distinct values for a specified field across a collection.

Sample Documents

To follow along with the examples in this guide, use the following code snippet to insert documents that describe restaurants into the myDB.restaurants collection:

const myDB = client.db("myDB");
const myColl = myDB.collection("restaurants");
await myColl.insertMany([
  { "_id": 1, "restaurant": "White Bear", "borough": "Queens", "cuisine": "Chinese" },
  { "_id": 2, "restaurant": "Via Carota", "borough": "Manhattan", "cuisine": "Italian" },
  { "_id": 3, "restaurant": "Borgatti's", "borough": "Bronx", "cuisine": "Italian" },
  { "_id": 4, "restaurant": "Tanoreen", "borough": "Brooklyn", "cuisine": "Middle Eastern" },
  { "_id": 5, "restaurant": "Äpfel", "borough": "Queens", "cuisine": "German" },
  { "_id": 6, "restaurant": "Samba Kitchen", "borough": "Manhattan", "cuisine": "Brazilian" },
]);

Note

Your query operation may return a reference to a cursor that contains matching documents. To learn how to examine data stored in the cursor, see the Cursor Fundamentals page.

Distinct

The distinct() method requires a document field as a parameter. You can specify the following optional parameters to adjust the method output:

  • A query parameter to refine your results

  • An options parameter to set collation rules

Document Field Parameter

Pass the name of the document field to return a list of the field's unique values.

Example

The "Queens" and "Manhattan" borough values each appear more than once in the sample documents. However, the following example retrieves the unique values of the borough field:

// specify "borough" as the field to return values for
const cursor = myColl.distinct("borough");
for await (const doc of cursor) {
  console.dir(doc);
}

This code outputs the following borough values:

[ "Bronx", "Brooklyn", "Manhattan", "Queens" ]

Query Parameter

You can specify a query parameter to return unique values for documents that match your query.

Visit Specify a Query for more information on constructing a query filter.

Example

The following example outputs the distinct values of the cuisine field but excludes restaurants in "Brooklyn":

// exclude Brooklyn restaurants from the output
const query = { borough: { $ne: "Brooklyn" }};
// find the filtered distinct values of "cuisine"
const cursor = myColl.distinct("cuisine", query);
for await (const doc of cursor) {
  console.dir(doc);
}

In this case, the query filter matches every borough value except for "Brooklyn". This prevents distinct() from outputting one cuisine value, "Middle Eastern". The code outputs the following values:

[ "Brazilian", "Chinese", "German", "Italian" ]

Options Parameter

You can specify the collation to the distinct() method by defining a collation field as an options parameter. This field allows you to set regional rules for string ordering and comparisons.

See Collations for instructions on applying collations.

Note

When using the options parameter, you must also specify a query parameter. If you don't want to use a query filter, define the query as {}.

Example

The following example uses a collation field to specify German language ordering conventions when outputting the distinct restaurant values:

// define an empty query document
const query = {};
// specify German string ordering conventions
const options = { collation: { locale: "de" }};
const cursor = myColl.distinct("restaurant", query, options);
for await (const doc of cursor) {
  console.dir(doc);
}

In this case, German string ordering conventions place words beginning with "Ä" before those beginning with "B". The code outputs the following:

[ "Äpfel", "Borgatti's", "Samba Kitchen", "Tanoreen", "Via Carota", "White Bear" ]

Without specifying a collation field, the output order would follow default binary collation rules. These rules place words beginning with "Ä" after the those with unaccented first letters:

[ "Borgatti's", "Samba Kitchen", "Tanoreen", "Via Carota", "White Bear", "Äpfel" ]

Additional Information

For a runnable example of retrieving distinct values, see Retrieve Distinct Values of a Field.

API Documentation

To learn more about the distinct() method and its parameters, you can visit the API documentation.

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