28 Working with List: map and flatMap

 

After reading this lesson, you will be able to:

  • Transform the elements of a sequence using the map function
  • Simplify a nested structure using the flatten method
  • Manipulate and combine lists using the flatMap operation
  • Chain instances of List using for-comprehension

In the previous lesson, you have learned the basics of the type List of the Scala Standard Collection library. In this lesson, you’ll learn about the basic operations you can perform on lists similar to those you have seen for the class Option. You will see how to use the map operation to apply a function to a sequence’s elements, unify nested lists using flatten, and chain them together using flatMap. You’ll learn how to use for-comprehension to combine and manipulate multiple lists into one. In the capstone, you will use the operations to extract information from the Movies Dataset.

Consider this

Imagine you need to traverse and apply a function to every element of a list. How would you implement it?

28.1  The map, flatten, and flatMap operations

In the previous lesson, you have represented the contacts of your address book using the following representation:

case class Contact(name: String, surname: String, number: String)

28.1.1    The map function

28.1.2    The flatten function

28.1.3    The flatMap function

28.2  For-comprehension

28.3  Summary

28.4  Answers to Quick Checks