Motivation

Before we start learning about immutable and mutable collections in Scala, we'll try to solve a simple problem using powerful methods provided by Scala collections. For that, let's take a look at a scenario:

RESTful APIs

As shown in the preceding image, we have a set of APIs with method types such as GET, POST, and PUT, and their associated URIs. As these are two entities (method and URI), think of all these as a list of tuples. Now we want to segregate them, so we can create a map, as shown in the right column of the preceding image. A map is a collection that stores values in a key-value pair. Hence, on the right side you can see API information as key-value pairs, where key is the method name, and the value is a list of URIs for that particular request type. So, the idea is to convert List[(String, String)] to Map[String, List[String]]. You may want to think about the solution, and come up with your own.

Meanwhile, let's see if Scala helps us in any way with our solution:

object...