db={"qr":[{"qrId":"0PRA","owner":"1","qrName":"Campaign 0PRA","qrCategory":"html","shortUrl":"http://someurl.com/0PRA"},{"qrId":"NQ17","owner":"2","qrName":"Campaign NQ17","qrCategory":"menu","shortUrl":"http://someurl.com/NQ17"}],"data":[{"_id":"6200f2a8c0cf7a1c49233c7f","qrId":"0PRA","device":"iOS","city":"Beijing"},{"_id":"6200f2eac0cf7a1c49233c80","qrId":"0PRA","device":"AndroidOS","city":"Beijing"},{"_id":"6200f3a4c0cf7a1c49233c81","qrId":"0PRA","device":"AndroidOS","city":"Beijing"},{"_id":"6200f632c0cf7a1c49233c88","qrId":"0PRA","device":"AndroidOS","city":"Nanchang"},{"_id":"6201b342c0cf7a1c49233caa","qrId":"0PRA","device":"iOS","city":"Taizhou"},{"_id":"6200f207c0cf7a1c49233c7a","qrId":"NQ17","device":"iOS","city":"Singapore"},{"_id":"8200f207c1cf7a1c49233c7a","qrId":"NQ17","device":"iOS","city":"Singapore"},{"_id":"6200ac5db44f23b9ec2b6040","qrId":"NQ17","device":"AndroidOS","city":"San Antonio"}]}

db.qr.aggregate([{"$match":{owner:{"$in":["1","2"]}}},{"$lookup":{"from":"data","localField":"qrId","foreignField":"qrId","as":"data","pipeline":[{"$facet":{"deviceGroup":[{"$group":{"_id":"$device","sum":{"$sum":1}}},{"$sort":{sum:-1}},{"$limit":1}],"cityGroup":[{"$group":{"_id":"$city","sum":{"$sum":1}}},{"$sort":{sum:-1}},{"$limit":1}],"all":[]}}]}}])