Kotlin Collections Deep Dive: List & MutableList Operations

In Kotlin, List is a collection of ordered elements. You can create mutable or immutable lists depending on whether you want to change the list after it's created.

Creating Lists

val numbers = listOf(1, 2, 3, 4, 5)         // Immutable
val fruits = mutableListOf("Apple", "Banana", "Mango") // Mutable

Immutable List

val fruits = listOf("Apple", "Banana", "Orange")
println(fruits[0]) // Output: Apple

Mutable List

val numbers = mutableListOf(1, 2, 3)
numbers.add(4)
println(numbers) // Output: [1, 2, 3, 4]

Immutable List operations

val list = listOf("a", "b", "c")

println(list[0])              // Access element by index
println(list.size)            // Get size
println("b" in list)          // Check if item exists
println(list.indexOf("c"))    // Find index
println(list.contains("a"))   // Check presence
println(list.first())         // Get first element
println(list.last())          // Get last element

MutableList operations

val list = mutableListOf("a", "b", "c")

list.add("d")                 // Add element
list.remove("b")              // Remove element by value
list.removeAt(0)              // Remove by index
list[0] = "z"                 // Update element
list.clear()                  // Remove all
list.addAll(listOf("x", "y")) // Add multiple

Looping over a List

for (item in list) {
    println(item)
}

list.forEach { println(it) }

Higher-order functions

val numbers = listOf(1, 2, 3, 4, 5)

val doubled = numbers.map { it * 2 }              // Transform
val even = numbers.filter { it % 2 == 0 }         // Filter
val sum = numbers.reduce { acc, i -> acc + i }    // Sum up
val found = numbers.find { it > 3 }               // Find first match

Access Elements

val first = list[0]
val last = list.last()
val size = list.size
val isEmpty = list.isEmpty()

Iterate Over List

for (item in list) {
    println(item)
}

list.forEach {
    println(it)
}

Add / Remove (for MutableList)

val list = mutableListOf("A", "B")

list.add("C")             // Add single item
list.addAll(listOf("D"))  // Add multiple items

list.remove("B")          // Remove item by value
list.removeAt(0)          // Remove item by index
list.clear()              // Remove all items

Update Elements

list[1] = "Z"   // Update value at index

Filter & Transform

val filtered = list.filter { it.startsWith("A") }
val uppercased = list.map { it.uppercase() }

Search

val containsA = list.contains("A")
val index = list.indexOf("C")
val found = list.find { it == "B" }

Sorting

val sorted = list.sorted()
val reversed = list.reversed()
val customSort = list.sortedBy { it.length }

Sublist & Slice

val sub = list.subList(1, 3)      // From index 1 to 2
val slice = list.slice(0..1)

Distinct / Union / Intersect

val distinct = listOf("A", "A", "B").distinct()
val union = listOf("A", "B").union(listOf("B", "C"))
val intersect = listOf("A", "B").intersect(listOf("B", "C"))

Convert Between List & Other Types

val array = list.toTypedArray()
val set = list.toSet()
val joined = list.joinToString(", ")