The Problem• We want to recommend content to a user which was viewed by his friends recently.• But we can’t recommend a user everything his friends viewed because we have limited display space.• And there is a privacy issue because a user’s friends might not want their viewing history exposed.
The Solution• Rank the slideshows viewed recently by a user’s friends using some metric.• Just show the top ranked slideshow from that list.• Display one slideshow per day to the user.
But what will be the ranking metric?• Suppose a user has 100 friends,• Each friend viewed 20 slideshows in the last week.• That gives us 100 X 20 = 2000 slideshows• Rank them according to the total number of views/favorites/comments the slideshow got.
How will we know the correctness of the metric? By measuring the CTR.
But where will we display these recommendations? In the newsfeed/profile page
What about privacy?The solution to privacy is anonymizing
But what is anonymizing ?• It means hiding personal data about an entity.• Show the heading “Slideshow S Viewed by one of your friends”• Never show “Slideshow S Viewed by your friend Mr. X”• Because we don’t want to make Mr. X upset.