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.
RDDs can hold key/value pairs in addition to just single values. In our previous examples, we looked at RDDs that included lines of text for an input data file or that contained movie ratings. In those cases, every element of the RDD contained a single value, either a line of text or a movie rating, but you can also store more structured...