MongoDB Aggregation $group

Aggregation $group

This aggregation stage groups documents by the unique _id expression provided.

Don't confuse this _id expression with the _id ObjectId provided to each document.

Example

In this example, we are using the "sample_airbnb" database loaded from the sample data in the Intro to Aggregations section.

db.listingsAndReviews.aggregate(
    [ { $group : { _id : "$property_type" } } ]
)

This will return the distinct values from the property_type field.