Array.reduce() / forEach() / enumerated()

// Aggregate (specify an initial value and a combining closure)
array.reduce(initialValue) { accumulated, element in
    return newAccumulatedValue
}
array.reduce(0, +)  // Concise form using an operator

// Iterate over all elements (no return value)
array.forEach { element in
    // process
}

// Enumerate with index
for (index, element) in array.enumerated() { }

// Pair elements from two arrays
zip(array1, array2)

// reduce: calculate the sum
let numbers = [1, 2, 3, 4, 5]
let sum = numbers.reduce(0) { $0 + $1 }
print(sum)  // 15

// Concise form using an operator
let sumShort = numbers.reduce(0, +)
print(sumShort)  // 15

// Find the maximum value
let maxVal = numbers.reduce(Int.min) { max($0, $1) }
print(maxVal)  // 5

// reduce(into:): build a dictionary
let words = ["apple", "banana", "apricot", "blueberry", "avocado"]
let grouped = words.reduce(into: [Character: [String]]()) { dict, word in
    let key = word.first!
    dict[key, default: []].append(word)
}
print(grouped["a"] ?? [])  // ["apple", "apricot", "avocado"]
print(grouped["b"] ?? [])  // ["banana", "blueberry"]

// forEach: process all elements
["Swift", "Kotlin", "Rust"].forEach { lang in
    print("Language: \(lang)")
}

// enumerated: iterate with index
let fruits = ["apple", "orange", "grape"]
for (i, fruit) in fruits.enumerated() {
    print("\(i + 1). \(fruit)")
}

// zip: pair elements from two arrays
let names = ["Taro", "Hanako", "Jiro"]
let scores = [85, 92, 78]
for (name, score) in zip(names, scores) {
    print("\(name): \(score) points")
}

forEach is equivalent to a for-in loop, but because it uses a closure, you cannot use break or continue inside it. If you need to stop iteration early, use a for-in loop instead.

reduce(into:) is more efficient than the standard reduce when building a dictionary or array as the result. zip stops at the shorter sequence. If the two arrays have different lengths, the extra elements are silently discarded.

For searching arrays, see array.contains() / firstIndex() / lastIndex().