Database
[{"country":"UK","business":"computer","companies":24},{"country":"UK","business":"automotive","companies":12},{"country":"US","business":"medical","companies":3},{"country":"US","business":"food","companies":53}]
Query
db.collection.aggregate([{$group:{_id:"$country",business:{$addToSet:"$business"}}},{$project:{_id:0,res:[{k:"$_id",v:{business:"$business"}}]}},{$replaceRoot:{newRoot:{"$arrayToObject":"$res"}}}])