List — zip() / unzip()

val names = listOf("Alice", "Bob", "Carol")
val scores = listOf(85, 72, 91)

// zip — pairs corresponding elements into Pair objects.
val zipped = names.zip(scores)
// [Pair("Alice", 85), Pair("Bob", 72), Pair("Carol", 91)]

// zip with transform — applies a custom transformation.
val results = names.zip(scores) { name, score -> "$name: $score points" }

// unzip — splits a list of Pairs back into two lists.
val (n, s) = zipped.unzip()  // restores names and scores.

fun main() {
    // Basic zip
    val names = listOf("Alice", "Bob", "Carol", "Dave")
    val scores = listOf(85, 72, 91, 68)
    val ages = listOf(25, 30, 28)  // truncated to the shorter length (3 items)

    val zipped = names.zip(scores)
    println("zip: $zipped")

    // zip with transform
    val results = names.zip(scores) { name, score ->
        "$name: ${score} points (${if (score >= 80) "Pass" else "Fail"})"
    }
    results.forEach { println(it) }

    println()

    // Different lengths (truncated to the shorter list)
    val nameAge = names.zip(ages)
    println("Different length zip: $nameAge")  // 3 items

    println()

    // unzip — splits Pairs back into two lists.
    val (nameList, scoreList) = zipped.unzip()
    println("Names: $nameList")
    println("Scores: $scoreList")

    println()

    // zipWithNext — creates pairs of adjacent elements (for computing differences)
    val temps = listOf(20.0, 22.5, 19.0, 25.0, 23.0)
    println("Temperature changes:")
    temps.zipWithNext { today, tomorrow ->
        val diff = tomorrow - today
        val dir = if (diff > 0) "↑" else if (diff < 0) "↓" else "→"
        println("  ${today}°C $dir ${tomorrow}°C (${"%.1f".format(diff)})")
    }

    println()

    // Zipping 3 lists (using zip twice)
    val first = listOf(1, 2, 3)
    val second = listOf("a", "b", "c")
    val third = listOf(true, false, true)
    val triple = first.zip(second).zip(third) { (a, b), c -> Triple(a, b, c) }
    triple.forEach { println(it) }
}

zip() is useful when you want to process two lists in parallel. If the lists have different lengths, the result is truncated to the shorter one — no exception is thrown.

zipWithNext() is useful for computing differences or rates of change between consecutive elements. It replaces index-based for loops.

For flattening lists, see Lists — flatMap() / flatten(). For folding, see Lists — reduce() / fold().