How can I protect data from other users when they are necessary for comparing with current user in the front-end implementation of a website?

I have to develop a web page which presents a user's profile list of achievements. Some achievements depend on comparison with data from other users. I don't have access to the code that runs server-side. I can only request data from any user I want. Is it possible to make it so data from other users don't leak? How can I process the data from other users to calculate the current user achievements without making it possible for the user to access other users' data? I'm using AngularJS for data-binding.