distinct, distinctBy, intersect, union

fun main() {
    val xs = listOf(1, 2, 2, 3, 3, 3, 4)

    println(xs.distinct())                              // [1, 2, 3, 4]

    // distinctBy — dedupe by something derived
    val users = listOf("Alice@x.com", "BOB@x.com", "alice@X.com", "Carol@x.com")
    val uniqueByLower = users.distinctBy { it.lowercase() }
    println(uniqueByLower)                              // [Alice@x.com, BOB@x.com, Carol@x.com]

    // Set ops on lists
    val a = listOf(1, 2, 3, 4)
    val b = listOf(3, 4, 5, 6)
    println(a.union(b))                                 // [1, 2, 3, 4, 5, 6]
    println(a.intersect(b))                             // [3, 4]
    println(a.subtract(b))                              // [1, 2]

    // Element-level membership
    println(3 in a)                                     // true
}