Arraylet arr = [1,2,3,4,5] let arr1 = arr.map { i in i * 100

let arr = [1,2,3,4,5]

let arr1 = arr.map { i in

i * 100

}

// 过滤

let arr2 = arr.filter { i in

return i > 2

}

arr.reduce(0) { result, elem in

return result + elem

}

arr.reduce(0) { $0 +$ 1}

print(arr2)

 let arr = Array.init(repeating: 5, count: 3)打印[5, 5, 5]



        var arr = [1,2,3]        var arr1 = arr.map{Array.init(repeating: $0, count: $0)}
        var arr2 =  arr.flatMap{Array.init(repeating: $0, count: $0)}
// 可以过滤nil 去除optional
        arr.compactMap(Int($0))



 
 var arr = [1,2,3]
        调用时候才加载
        arr.lazy.map { i in
            
        }

map 如果调用对象为nil 直接返回nil

flagMap 可以判断是否可选类型，是的话不会再做一层包装如果内部是函数会将返回值传递到函数中去