[{"_id":ObjectId("5a934e000102030405000000"),"sides":{"0":{"dist":10},"1":{"dist":10}}},{"_id":ObjectId("5a934e000102030405000001"),"sides":{"0":{"dist":100}}}]

db.collection.aggregate([{"$project":{"sides_array":{"$objectToArray":"$sides"}}},{"$unwind":"$sides_array"},{"$match":{"sides_array.v.dist":10}},{"$group":{"_id":"$_id","sides":{"$push":"$sides_array"}}},{"$project":{"_id":1,"sides":{"$arrayToObject":"$sides"}}}])