Frank Kane's Taming Big Data with Apache Spark and Python

Creating a key/value RDD

Syntactically, there's nothing really special about key/value RDDs, it's all kind of magic in Python. If you are storing a list of two items as your values in the RDD, then it is a key/value RDD and you can treat it as such. Here's a simple example:

totalsByAge = rdd.mapValues(lambda x: (x, 1)) 

If I want to create a totalsByAge RDD out of an original RDD that contains a single value in each element, my lambda function here, x, can take each rating or each number, whatever happens to be x, and transform that into a pair of the original number and then the number 1. So the syntax with the parentheses indicates that this is a single entity as far as Python is concerned, but it consists of two elements; it's a list ...