Kotlin Collections

val names = listOf("Ram", "Sita", "Hari")     // immutable
val mutable = mutableListOf("Ram")             // mutable
mutable.add("Sita")

// Operations
val upper = names.map { it.uppercase() }       // ["RAM", "SITA", "HARI"]
val short = names.filter { it.length <= 3 }    // ["Ram"]
val found = names.find { it.startsWith("S") }  // "Sita"
val sorted = names.sorted()                     // ["Hari", "Ram", "Sita"]

val scores = mapOf(
    "Ram" to 85,
    "Sita" to 92,
    "Hari" to 78
)

println(scores["Ram"])         // 85
println(scores.getOrDefault("Gita", 0))  // 0

val upper = scores.mapValues { (_, v) -> v + 5 }
// {Ram=90, Sita=97, Hari=83}

val unique = setOf(1, 2, 3, 2, 1)  // {1, 2, 3}
val a = setOf(1, 2, 3)
val b = setOf(3, 4, 5)
println(a union b)         // {1, 2, 3, 4, 5}
println(a intersect b)    // {3}

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

numbers.filter { it % 2 == 0 }  // [2, 4]
numbers.map { it * it }         // [1, 4, 9, 16, 25]
numbers.reduce { acc, n -> acc + n }  // 15
numbers.take(3)                 // [1, 2, 3]
numbers.drop(2)                 // [3, 4, 5]
numbers.any { it > 3 }          // true
numbers.all { it > 0 }          // true

val students = listOf("Ram" to "A", "Sita" to "B", "Hari" to "A")
val grouped = students.groupBy { it.second }
// {A=[Ram, A], B=[Sita, B]}

val partitioned = numbers.partition { it > 3 }
// Pair([4, 5], [1, 2, 3])