[{"_id":"5fc73e7131e6a20f6c492178","participants":[{"_id":"5fc74bc5e7c54d0ea8f133ca","rsvp":"Yes","name":"Participant 1","email":"participant1@gmail.com"},{"_id":"5fc74e1254b8d337b4ae36d2","rsvp":"Not Answered","name":"Participant 2","email":"participant2@gmail.com"}],"title":"Meeting 1","startTime":"2020-11-01T18:30:00.000Z","endTime":"2020-11-03T18:30:00.000Z"},{"_id":"5fc73f1cdfc45d3ca0c84654","participants":[{"_id":"5fc74bc5e7c54d0ea8f133ca","rsvp":"Yes","name":"Participant 2","email":"participant2@gmail.com"}],"title":"Meeting 2","startTime":"2020-11-01T18:30:00.000Z","endTime":"2020-11-03T18:30:00.000Z"}]

db.collection.aggregate([{"$unwind":"$participants"},{$group:{_id:"$participants._id",participants:{$first:"$participants"},meetings:{"$addToSet":"$title"}}}])