lambda.swift

/ 条件にマッチする要素のみを取り出したい場合
func filter(array: []) {
    let newArray = array.filter { $0 < 3 }
    // newArray -> [1,2]
}

// 各要素に対して処理を行い、かつ戻り値が必要ない場合
func forEach(array: []) {
    array.forEach {
        print("\($0)")
    }
}

let array = [1,2,3,4,5]
 
// 配列内の要素に処理を適用し、その処理を施した配列を使いたい場合
func map(array: []) {
    let newArray = array.map { $0 * 5 }
    // newArray -> [5, 10, 15, 20, 25]    
}
 
func map_dictionary() {
    let celsius = ["Tokyo":14.0, "Osaka":17.0, "Okinawa":26.0]
    let fahrenheit = celsius.map { ($0.0, 1.8 * $0.1 + 32) }
    // fahrenheit -> [("Okinawa", 78.8), ("Tokyo", 57.2), ("Osaka", 62.6)]
}

/ 要素使って結果を集計したいような場合
func reduce(array: []) {
    let i = array.reduce(0) { (num1, num2) -> Int in
        num1 + num2
    }
    // i -> 15
}
 
func reduce_2(array:[]) {
    let s = array.reduce(0, combine: +) 
    // s -> 15
    let k = array.reduce(1, combine: *) 
    // k -> 120    
}
 
func reduce_dictionary() {
	let queries = ["id=3", "token=abc", "tag=5"]
 
	let params = queries.reduce([String: String]()) { (var dict, q) in
		// qに各要素が順番にくる
		// (dict, q) = ([], "id=3")
		// (dict, q) = (["id": "3"], "token=abc")
		// (dict, q) = (["id": "3", "token": "abc"], "tag=5")
    	let v = q.componentsSeparatedByString("=")
    	let (key, value) = (v[0], v[1])
    	dict[key] = value
    	return dict
    }
	// params -> ["id": "3", "token": "abc", "tag": "5"]
}