In this chapter we will see ways of changing the format of the data. In the real world, an observable may be of any type. It is uncommon that the data is already in format that we want them in. More likely, the values need to be expanded, trimmed, evaluated or simply replaced with something else.

This will complete the three basic categories of operations. `map` and `flatMap` are the fundamental methods in the third category. In literature, you will often find them refered to as "bind", for reasons that are beyond the scope of this guide.

In the last chapter we introduced an implementation of `Subscriber` for convenience. We will continue to use it in the examples of this chapter.