[{"_id":"xw5vk1s_PpJaal46di","users":["xw5vk1s",/**first element equivalent to from*/"PpJaal46di"/**equivalent to previously to*/],"like":true},{"_id":"xw5vk1s_PpJaal46dj","users":["PpJaal46di","xw5vk1s"],"like":true}]

db.collection.aggregate([{$match:{users:"xw5vk1s"}},{$group:{_id:{$sortArray:{input:"$users",sortBy:1}},count:{$sum:1}}},{"$match":{count:{$gt:1}}}])