Examples of Kotlin Collections Manipulation

Explore practical examples of Kotlin collections manipulation for efficient programming.
By Jamie

Understanding Kotlin Collections Manipulation

Kotlin provides a rich set of collection types, including lists, sets, and maps, that allow for easy manipulation of data. This article presents three practical examples of Kotlin collections manipulation that showcase how to efficiently work with collections in real-world scenarios.

Example 1: Filtering a List of Numbers

Context

In many applications, you may need to filter out specific elements from a list. This example demonstrates how to filter even numbers from a list of integers.

fun main() {
    val numbers = listOf(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
    val evenNumbers = numbers.filter { it % 2 == 0 }
    println(evenNumbers) // Output: [2, 4, 6, 8, 10]
}

In this code, the filter function is used to create a new list containing only the even numbers from the original list. The lambda expression it % 2 == 0 checks whether each number is even.

Notes

  • This method can be easily modified to filter for other conditions, such as odd numbers or numbers greater than a specific value.

Example 2: Grouping a List of Employees by Department

Context

When working with a list of objects, such as employees, you may want to group these objects based on a specific property. This example illustrates grouping employees by their department.

data class Employee(val name: String, val department: String)

fun main() {
    val employees = listOf(
        Employee("Alice", "HR"),
        Employee("Bob", "IT"),
        Employee("Charlie", "IT"),
        Employee("Daisy", "HR"),
        Employee("Eve", "Marketing")
    )

    val groupedByDepartment = employees.groupBy { it.department }
    println(groupedByDepartment)
    // Output: {HR=[Employee(name=Alice, department=HR), Employee(name=Daisy, department=HR)], IT=[Employee(name=Bob, department=IT), Employee(name=Charlie, department=IT)], Marketing=[Employee(name=Eve, department=Marketing)]}
}

In this example, the groupBy function groups the employees based on their department. The output is a map where each key is a department name, and the value is a list of employees belonging to that department.

Notes

  • You can easily extend this example to sort the employees within each department or apply additional transformations.

Example 3: Merging Two Maps

Context

In scenarios where you have multiple data sources, you may need to merge information from two maps. This example demonstrates how to merge two maps while handling duplicate keys by summing their values.

fun main() {
    val map1 = mapOf("A" to 1, "B" to 2, "C" to 3)
    val map2 = mapOf("B" to 3, "C" to 4, "D" to 5)

    val mergedMap = (map1 + map2).entries.groupBy({ it.key }, { it.value })
        .mapValues { it.value.sum() }

    println(mergedMap)
    // Output: {A=1, B=5, C=7, D=5}
}

In this code snippet, the + operator combines the two maps. The groupBy function is used to handle duplicate keys, and mapValues sums the values for each key.

Notes

  • You can modify the merge logic to handle duplicates differently, such as taking the maximum or minimum value instead of summing.

These examples of Kotlin collections manipulation highlight the versatility and power of Kotlin in managing data efficiently. By leveraging these techniques, you can write cleaner and more effective Kotlin code.