Exercise

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.

Instructions

100 XP

$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.