Facebook has an ingrained algorithm that keeps track of exactly how you communicate with your friends and then types appropriately. Source
Friends List On Facebook Order
While the exact ranking formula is secret, it does take into consideration the list below aspects:
* Exactly how often you visit your friends' profiles
* How commonly you click your friends' web links
* Photos/tags in common
* Usual teams/ associations
* utual Friends
* Exactly how often you look for friends
* Relative popularity (exactly how prominent your friends are among your shared links).
So, the actual sorting is not arbitrary, however rather thoroughly crafted to help with interaction and also site engagements.
