Mongodb, grouping values only once

I am new to mongodb, I have a collection of people and some of them have a value that I am interested in ("val"). For everyone who has that value, I would like to have a list of another value ("potential") without repeating.

{ "_id" : 001, "val" : true, "potential", 100}
{ "_id" : 002, "val" : true, "potential", 200}
{ "_id" : 003, "val" : true, "potential", 200}
{ "_id" : 004, "potential" : 300}
{ "_id" : 005, "potential" : 400}

I would like to get

{"values" : [100, 200]}

Thank you very much

>Solution :

To achieve this, you can use the MongoDB aggregation framework with a pipeline that has the following stages:

1. $match: filter the documents to only include those with "val" equal to true.
2. $group: group the documents by the "potential" field and create an array of unique values for each group using the $addToSet operator.
3. $project: reshape the output to return only the array of "potential" values.
   Here’s an example of the MongoDB aggregation pipeline:

db.collection.aggregate([
  {
    $match: { val: true }
  },
  {
    $group: {
      _id: null,
      potentials: { $addToSet: "$potential" }
    }
  },
  {
    $project: {
      _id: 0,
      values: "$potentials"
    }
  }
])

This will return a document with a single field "values" containing an array of unique "potential" values for documents with "val" equal to true:

{ "values" : [100, 200] }

I hope this helps!