Countries of birth by prize category

Some prize categories have laureates hailing from a greater number of countries than do other categories. You will build an aggregation pipeline for the prizes collection to collect these numbers, using a $lookup stage to obtain laureate countries of birth.

This exercise is part of the course

Introduction to MongoDB in Python

View Course

Exercise instructions

$unwind the laureates array field to output one pipeline document for each array element.
After pulling in laureate bios with a $lookup stage, unwind the new laureate_bios array field (each laureate has only a single biography document).
Collect the set of bornCountries associated with each prize category.
Project out the size of each category's set of bornCountries.

Hands-on interactive exercise

Have a go at this exercise by completing this sample code.

pipeline = [
    # Unwind the laureates array
    {____: "$laureates"},
    {"$lookup": {
        "from": "laureates", "foreignField": "id",
        "localField": "laureates.id", "as": "laureate_bios"}},

    # Unwind the new laureate_bios array
    {"$unwind": ____},
    {"$project": {"category": 1,
                  "bornCountry": "$laureate_bios.bornCountry"}},

    # Collect bornCountry values associated with each prize category
    {"$group": {____: "$category",
                "bornCountries": {"$addToSet": "$bornCountry"}}},

    # Project out the size of each category's (set of) bornCountries
    {"$project": {"category": 1,
                  "nBornCountries": {"$size": ____}}},
    {"$sort": {"nBornCountries": -1}},
]
for doc in db.prizes.aggregate(pipeline): print(doc)

Edit and Run Code