var arr = [1, 2, 3]//map函數是有返回值的，想要arr里面的值map過去需要arr重新接收新值arr.map { (a : Int) -> Int in  return a * 2}//這種寫法只是尾隨閉包的簡寫。。arr = arr.map {  $0 * 2}

//floatMap函數可以降維var arr1 = [[1, 2], [4, 5], [6, 7]]var aaa = arr1.flatMap {  $0}//floatMap函數去空作用,還會解包數據var arr2 = ["swift", nil, "java"]var bbb = arr2.flatMap {  $0}

//filter 函數用作對容器內元素進行篩選var arr3 = ["swift", "java", "oc", "python"]arr3 = arr3.filter {  guard $0.characters.count > 2 else {    return false  }  return true}

//reduce 函數用作對容器內元素進行操作，將元素字符串拼接var arr4 = [2, 3, 4, 5]//arr4.reduce("", {//  return $0 == "" ? String($1) : $0 + String($1)//})//用reduce求和arr4.reduce(0) {  return $0 + $1}// 將數組中的每個字符串用‘,'拼接let arr5 = ["Objective-C", "Swift", "HTML", "CSS", "JavaScript"]// $0表示計算后的結果, $1表示數組中的每一個元素arr5.reduce("", {  return $0 == "" ? $1 : $0 + "," + $1})