http://ask.metafilter.com/134353/How-does-Facebook-generate-the-list-of-friend-icons-on-the-left-side-of-my-profile-screen

Questions : 

How does it decide which ones to display? Does it pick people who've visited my profile lately? Or people whose profiles I've visited? Does it try to mix up people from a variety of groups -- these ones from high school, these from that online group, a certain amount of men, a certain amount of women? I have a hard time believing that the process is entirely random because I've noticed some friend icons appear only at certain points during the week and never appearing during other times of the week. 

Selected Answers : 

- My unsubstantiated speculation is that it's largely random, though somewhat weighted by a "rank" assigned to your friends, affected largely by how active they are and how closely intertwined your social graphs are.

For a company that collects as much data about its users as Facebook does, I strongly doubt anything there is truly random.

- Best as I can tell, it's a mix of who's online at a given time, who posts the most on your wall/status/photos and who visits your profile most often. I think this is seeded with totally random picks to make everything seem all that more difficult to discern. I have a fan page on facebook as well as a profile and I've noticed that everytime I look at it, the "fans" section shows me three people I am personally friends with and three strangers I am NOT friends with. So there is some smart stuff going on there.

- I think it's a mix of both a little bit of random and the mutual friends of someone visiting your profile. I have noticed that, even with fan pages or friends with hundreds or thousands of friends, who shows up in the box is strongly weighted towards people I know. eg, if I visit a band with 10,000 fans, I have noticed that 3-4 of the 6 fans shown are often my friends.

- FWIW humans are terrible at deciding whether things are random. We are so predisposed to find patterns in things that it's not unusual for people to claim they have found a pattern in random data, even after being told that it's random and shown the method of generation (qv lottery numbers, etc).

In other words, don't believe anyone who doesn't have the statistics to back it up :-)

- Of course, there's also the likelihood that if I'm your friend and visit your page, the six (non-mutual) featured friends that I see might be a result of a whole 'nother algorithm.

But I'm curious about chrisamiller's comment, that the suggested friends are more obviously not randomly posted. I do seem to notice one name more often than others, but it could just be confirmation bias, and I don't have any mutual friends with said person. Can anyone elaborate on that?

완전히 random하진 않을듯. 찾아보니 페이스북 FAQ에 답이 있었다.

Since the implementation of the New Profile Layout in December 2010, Facebook uses a specific method to select which friends appear on your profile. The method is explained in the following paragraph from one of its Help Center pages:

“Friends who you publicly interact with the most appear first on your profile. Examples of public interactions include Wall posts, comments and mutually attended events — Facebook will never show friends based on whose profiles you choose to view or who you interact with over messages and chat.”

As Facebook has stated many times that it makes technically impossible to know who views whose profile, that information is not used to select the friends that appear first.

http://romcartridge.blogspot.com/2010/12/how-does-facebook-select-which-friends.html

http://www.facebook.com/help/new/?page=771