**Course Title:** Kotlin Programming: From Basics to Advanced Techniques **Section Title:** Working with Collections **Topic:** Introduction to collections: Lists, Sets, and Maps ### Overview of Collections In the previous topics, we've learned about control structures and functions. Now, we'll explore collections in Kotlin, which are used to store and manipulate data. Collections are essential in programming, as they allow you to work with multiple values at once. ### Lists A `List` is a collection that stores a ordered sequence of elements. In Kotlin, you can create a list using the `listOf()` function. ```kotlin val numbers = listOf(1, 2, 3, 4, 5) ``` You can access elements in a list using indexing. ```kotlin println(numbers[0]) // prints: 1 ``` Kotlin lists are immutable by default, meaning you cannot modify their contents once created. If you need a mutable list, use the `mutableListOf()` function. ```kotlin val mutableNumbers = mutableListOf(1, 2, 3, 4, 5) mutableNumbers.add(6) println(mutableNumbers) // prints: [1, 2, 3, 4, 5, 6] ``` ### Sets A `Set` is an unordered collection of unique elements. In Kotlin, you can create a set using the `setOf()` function. ```kotlin val uniqueNumbers = setOf(1, 2, 2, 3, 4, 4, 5) println(uniqueNumbers) // prints: [1, 2, 3, 4, 5] ``` Like lists, sets can be either immutable or mutable. ### Maps A `Map` is a collection that stores key-value pairs. In Kotlin, you can create a map using the `mapOf()` function. ```kotlin val colors = mapOf("red" to "#FF0000", "green" to "#00FF00") println(colors["red"]) // prints: #FF0000 ``` Maps can also be immutable or mutable. ### Key Concepts and Terminology * **Collection**: A group of objects that are stored and manipulated together. * **Immutable**: A collection that cannot be modified after creation. * **Mutable**: A collection that can be modified after creation. * **Indexing**: Accessing elements in a list or array using their position. * **Key-value pair**: A pair of values that are associated with each other in a map. ### Practical Takeaways * Use `listOf()` to create an immutable list and `mutableListOf()` to create a mutable list. * Use `setOf()` to create an immutable set and `mutableSetOf()` to create a mutable set. * Use `mapOf()` to create an immutable map and `mutableMapOf()` to create a mutable map. * Use indexing to access elements in a list or array. * Use key-value pairs to store and retrieve data in a map. ### Additional Resources * [Kotlin Documentation: Collections](https://kotlinlang.org/docs/collections-overview.html) * [Kotlin Language Specification: Collections](https://kotlinlang.org/spec/collections.html) ### Exercise Create a program that stores a list of names, a set of unique numbers, and a map of country codes and their corresponding names. Use indexing to access elements in the list and key-value pairs to retrieve data from the map. **Leave a comment below if you have any questions or need help with the exercise.** ### Next Topic In our next topic, we'll cover using collection functions: `filter()`, `map()`, and `reduce()` to perform common operations on collections.