Now that the meaning of the word "friend" can mean so much more (and so much less) than it did in years past, it's often hard to decide which relationships are actually worth keeping. If you're in an indecisive spot with your social circle, there's now an app called PPLKPR that measures your physiological responses to your friends, and it can help you out. Using a bluetooth-enabled heart rate monitor, PPLKPR allows you to "optimize your social life" by translating the biofeedback collected during your time spent with a person into emotions you can categorize.
The one problem with this idea is that friends don't always fall into simple groupings of "good" or "bad." Some of the best friends are those who tell you the hard truths, so it's probably possible to get "negative" physical reactions to even your favorite people. That said, if the app keeps telling you that you're "angry" while hanging out with a friend you've known for years, it could be just the evidence you need to refresh your social circle. Once all the basic data is collected, PPLKPR then helps you manage your relationships by suggesting you text friends who give you positive physiological responses. It also advises you to delete some people's contact info altogether — total burn. For those who prefer a scientific approach to life, it's hard to argue with that.