Kotlin Standard Library Cookbook

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We can also modify our map building operation to a more concise form by using the mapValues function:

fun getCoursesWithSubscribedStudents(): Map<Course, List<Student>> =        getStudents()                .flatMap { student ->                    student.courses.map { course -> course to student }                }                .groupBy { (course, _) -> course }                .mapValues { (course, courseStudentPairs) ->                    courseStudentPairs.map { it -> it.second }                }