[{"user_agent":"myapp v1.1(10)"},{"user_agent":"myapp v2.2(20)"},{"user_agent":"myapp v3.3(30)"},{"user_agent":"myapp v1.1(10) DEV"},{"user_agent":"xxxx"},{"user_agent":"yyyyy"},{"user_agent":"zzzz"}]

db.collection.aggregate([{"$match":{}},{"$group":{"_id":"$user_agent","count":{"$sum":1}}},{"$sort":{"_id":1}}])