Kotlin Standard Library Cookbook

Grouping data

The Kotlin standard library provides built-in support for the dataset group by operation. In this recipe, we are going to explore how to use it.

Let's assume we are working with the following types:

class Course(val name: String, val lecturer: Lecturer, val isPaid: Boolean = false)class Student(val name: String, val courses: List<Course>)class Lecturer(val name: String)

We also have a getStudents(): List<Student> function that returns a list of all the students from the database.

Given the getStudents(): List<Student> function, we are going to implement the getCoursesWithSubscribedStudents(): Map<Course, List<Student>> function responsible for extracting the map of all the courses students are subscribed to, and the list of ...