Overview
Within a collection, different documents might contain different values for a single field. For example, one restaurant document has a borough value of "Manhattan", and another has a borough value of "Queens". With PyMongo, you can retrieve all the distinct values that a field contains across multiple documents in a collection.
Sample Data
The examples in this guide use the sample_restaurants.restaurants collection from the Atlas sample datasets. To learn how to create a free MongoDB Atlas cluster and load the sample datasets, see the Get Started with PyMongo.
distinct() Method
To retrieve the distinct values for a specified field, call the distinct() method and pass in the name of the field you want to find distinct values for.
Retrieve Distinct Values Across a Collection
The following example retrieves the distinct values of the borough field in the restaurants collection. Select the Synchronous or Asynchronous tab to see the corresponding code:
results = restaurants.distinct("borough") for restaurant in results: print(restaurant)
Bronx Brooklyn Manhattan Missing Queens Staten Island
results = await restaurants.distinct("borough") for restaurant in results: print(restaurant)
Bronx Brooklyn Manhattan Missing Queens Staten Island
The results show every distinct value that appears in the borough field across all documents in the collection. Although several documents have the same value in the borough field, each value appears in the results only once.
Retrieve Distinct Values Across Specified Documents
You can provide a query filter to the distinct() method to find the distinct field values across a subset of documents in a collection. A query filter is an expression that specifies search criteria used to match documents in an operation. For more information about creating a query filter, see Specify a Query.
The following example retrieves the distinct values of the borough field for all documents that have a cuisine field value of "Italian". Select the Synchronous or Asynchronous tab to see the corresponding code:
results = restaurants.distinct("borough", { "cuisine": "Italian" }) for restaurant in results: print(restaurant)
Bronx Brooklyn Manhattan Queens Staten Island
results = await restaurants.distinct("borough", { "cuisine": "Italian" }) for restaurant in results: print(restaurant)
Bronx Brooklyn Manhattan Queens Staten Island
Modify Distinct Behavior
The distinct() method accepts optional parameters, which represent options you can use to configure the operation. If you don't specify any options, the driver does not customize the operation.
The following table describes the options you can set to customize distinct():
Property | Description |
|---|---|
| A query filter that specifies the documents to retrieve distinct values from. |
| An instance of ClientSession. |
| A comment to attach to the operation. |
| The maximum amount of time to allow the operation to run, in milliseconds. |
| An instance of Collation. |
The following example retrieves the distinct values of the name field for all documents that have a borough field value of "Bronx" and a cuisine field value of "Pizza". It also uses the comment option to add a comment to the operation. Select the Synchronous or Asynchronous tab to see the corresponding code:
results = restaurants.distinct("name", { "borough": "Bronx", "cuisine": "Pizza" }, comment="Bronx pizza restaurants" )
$1.25 Pizza 18 East Gunhill Pizza 2 Bros Aenos Pizza Alitalia Pizza Restaurant ...
results = await restaurants.distinct("name", { "borough": "Bronx", "cuisine": "Pizza" }, comment="Bronx pizza restaurants" )
$1.25 Pizza 18 East Gunhill Pizza 2 Bros Aenos Pizza Alitalia Pizza Restaurant ...
API Documentation
To learn more about any of the methods or types discussed in this guide, see the following API documentation: