mongodb get all unique values for each unique field

Question

I am looking to query a collection of property prices on mongodb. I would like to return the unique prices only. There are multiple entries for each property, but I want to return only the unique prices associated with the propertyID.

How would I structure the query to remove the duplicate values of price for each propertyID?

In the table below, there are 5 entries for the price of 400,000, and one for 425,000, for propertyID 752276. I would like to return just the two unique prices, but for all entries in the collection.

To further explain what I am looking for, If I had the object bellow, I would only want to return a:{10,20,30},b:{10,20}

a:{10,20,10,30}

b:{10,20,20,20}

Answer 1

You can achieve this with simple aggregation pipelines

{
   $group:{
    "_id": "$propertyID", //Group by property ID,
    "uniquePrices" : {
       "$addToSet" : "$price" //It will give you propertyID wise unique prices
    }
   }
}