Key/value RDDs and the average friends by age example

A powerful thing to do with RDDs is to put more structured data into it. One thing we can do is put key/value pairs of information into Spark RDDs and then we can treat it like a very simple database, if you will. So let's walk through an example where we have a fabricated social network set of data, and we'll analyze that data to figure out the average number of friends, broken down by age of people in this fake social network. We'll use key/value pairs and RDDs to do that. Let's cover the concepts, and then we'll come back later and actually run the code.