Collection Operations

fun main() {
    val numbers = listOf(5, 2, 8, 1)
    println("Sorted: ${numbers.sorted()}")
    println("Descending: ${numbers.sortedDescending()}")
}

fun main() {
    val numbers = listOf(1, 2, 3, 4, 5)
    println("First even: ${numbers.find { it % 2 == 0 }}")
    println("Any negative: ${numbers.any { it < 0 }}")
    println("All positive: ${numbers.all { it > 0 }}")
}

fun main() {
    val numbers = listOf(1, 2, 3, 4, 5, 6)
    println("Even count: ${numbers.count { it % 2 == 0 }}")
    println("Sum: ${numbers.sum()}")
    println("Sum of squares: ${numbers.sumBy { it * it }}")
}

fun main() {
    val words = listOf("apple", "banana", "avocado", "blueberry", "cherry")
    val grouped = words.groupBy { it.first() }
    println(grouped)
}

1. Writing a manual for loop to sort or search a collection when a clearer built-in function like .sorted() or .find() already exists.
2. Confusing .sorted() (returns a new sorted list) with .sort() (sorts a MutableList in place); using the wrong one on the wrong collection type.
3. Forgetting that many of these operations return a new collection rather than modifying the original in place.

• .sorted()/.sortedDescending() return a new list sorted in ascending/descending order.
• .find { } returns the first matching element or null; .any { }/.all { }/.none { } test conditions across the collection.
• .count { } counts matching elements; .sum()/.sumBy { } add up numeric values.
• Most of these operations return a new collection or value rather than mutating the original.