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 our 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.