My most common uses of map() & reduce()

Map&Reduce.swift

//
// #1 Adding things up
//

let numbers = [Int](0..<10)
let total = numbers.reduce(0) {
    return $0 + $1
}

struct Person {
    let name: String
    let age: Int
}

let people = [
    Person(name: "Katie",  age: 23),
    Person(name: "Bob",    age: 21),
    Person(name: "Rachel", age: 33),
    Person(name: "John",   age: 27),
    Person(name: "Megan",  age: 15)
]

let ages: [Int] = people.map { return $0.age }
let agesTotal   = ages.reduce(0) { return $0 + $1 }
let averageAge  = agesTotal / ages.count


//
// Combining booleans
//

let booleans = [
    false,
    false,
    true,
    false,
    true,
    true
]

let allTrue = booleans.reduce(true) {
    (sum, next) in
    return sum && next
}

let allFalse = booleans.reduce(true) {
    (sum, next) in
    return sum && !next
}

let anyTrue = booleans.reduce(false) {
    (sum, next) in
    return sum || next
}

let anyFalse = booleans.reduce(false) {
    (sum, next) in
    return sum || !next
}

struct OptionState {
    let title: String
    let selected: Bool
}

let optionStates = [
    OptionState(title: "Objective-C", selected: true),
    OptionState(title: "Swift",       selected: true),
    OptionState(title: "Haskell",     selected: false),
    OptionState(title: "Ruby",        selected: true)
]

let allSelected = optionStates.reduce(true) {
    return $0 && $1.selected
}

let anySelected = optionStates.reduce(false) {
    return $0 || $1.selected
}