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Retrieve Distinct Field Values
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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:
results = 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":
results = 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 |
|---|---|
filter | A query filter that specifies the documents to retrieve distinct
values from. |
session | An instance of ClientSession. |
comment | A comment to attach to the operation. |
maxTimeMS | The maximum amount of time to allow the operation to run, in
milliseconds. |
collation | 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.
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 ...
API Documentation
To learn more about any of the methods or types discussed in this guide, see the following API documentation: