Introduction to Enum.map

Welcome to this new unit about Elixir!

This final course focuses on building a TodoList application using Elixir. The course conists of 4 units, the last two units are about building the TodoList application. But before we start building the TodoList application, we will learn about more advanced topics in Elixir such as Enum.map, Enum.filter and Enum.reject. Let's get started!

Today, we will embark on an exciting journey to explore Enum.map, an important function in Elixir that empowers you to manipulate collections efficiently. As we delve into building a TodoList application, understanding Enum.map is your first step toward mastering list transformations in Elixir. Let's ensure you have a strong foundation to move forward confidently.

In this lesson, you'll learn the basics of Enum.map and how it can be used to update elements in a collection. This is a foundational concept in functional programming. Using Enum.map, you'll be able to traverse a list and apply changes to its elements, creating new lists reflecting those changes.

You will see Enum.map in action with a real-world example. Consider the following code from our lesson:

defmodule Student do
  defstruct id: nil, name: nil, grade: nil

  def update_grade(students, id, new_grade) do
    Enum.map(students, fn student ->
      if student.id == id do
        %Student{student | grade: new_grade}
      else
        student
      end
    end)
  end
end

defmodule Main do
  def run do
    students = [
      %Student{id: 1, name: "Alice", grade: 90},
      %Student{id: 2, name: "Bob", grade: 80},
      %Student{id: 3, name: "Charlie", grade: 70}
    ]

    tasks = Student.update_grade(students, 2, 85)
    IO.inspect(tasks)
  end
end

Main.run()

In this example, we define a list of Student structs, and then we use Enum.map to update the grade for a student with a specific ID. This action results in a new list with the updated grades. As a result students list will be updated with the new grade for the student with ID 2.

Let's understand the syntax for Enum.map and how it works in this example.

The Enum.map function takes two arguments: a list and a function. The function is applied to each element in the list, and the result is a new list with the transformed elements. In this example the first argument is the students list and the second argument is an anonymous function that takes a student as an argument and returns a new Student struct with the updated grade.

Now let's break down what Enum.map does in this example:

• Enum.map iterates over each element in the students list and applies the anonymous function to each element (student).
• In the anonymous function, we check if the id of the student matches the id we want to update which is passed as an argument to the update_grade function.
• If the id matches, we create a new Student struct with the updated grade.
• If the id does not match, we return the original student.

Thus, for each student in the list, we either return the original student or a new student with the updated grade. The result is a new list with the updated grades.