Swift 函数Count,Filter,Map,Reduce

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blog.csdn.net/hello_hwc

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前言：和OC不同，Swift有非常多全局的函数，这些全局函数对简化代码来说非常实用。眼下Swift出到了2.0,只是我这篇文章还是用Swift1.2写的演示样例代码。

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Count－统计数量

文档

func count<T : _CollectionType>(x: T) -> T.Index.Distance

Description
Return the number of elements in x.
O(1) if T.Index is RandomAccessIndexType; O(N) otherwise.

演示样例

 let arr = [1,2,3,4]
 let dic = [1:2,"a":"b"]
 let str = "Wenchenhuang"
 println(count(arr))//4
 println(count(dic))//2
 println(count(str))//12

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Filter－条件过滤

文档

func filter<S : SequenceType>(source: S, includeElement: (S.Generator.Element) -> Bool) -> [S.Generator.Element]

Description
Return an Array containing the elements of source, in order, that satisfy the predicate includeElement.

演示样例－过滤长度大于4的字符串

 let array = ["Wen","Chen","Huang"]
 let filteredArray =  filter(array, { (element:String) -> Bool in
     return count(element)>4;
  })
  println(filteredArray)

也能够简化

let filteredArray =  filter(array) {count($0)>4}

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Map - 映射集合类型，返回数组

文档

func map<C : CollectionType, T>(source: C, transform: (C.Generator.Element) -> T) -> [T]
Description 

Return an Array containing the results of mapping transform over source.

演示样例

let array = ["Wen","Chen","Huang"]
let mapedAray = map(array, { (element:String) -> Int in
    return count(element)
 })
 println(mapedAray) //［3，4。5］

相同能够简化

let mapedAray = map(array){count($0)}

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Reduce - 把数组结合到一起

文档

func reduce<S : SequenceType, U>(sequence: S, initial: U, combine: @noescape (U, S.Generator.Element) -> U) -U

Description
Return the result of repeatedly calling combine with an accumulated value initialized to initial and each element of `sequence`, in turn.

演示样例

 let array = ["Wen","Chen","Huang"]
 let reduceResult = reduce(array, "Hello ") { (originValue:String, element:String) -> String in
    return originValue + element;
 }
 println(reduceResult) //Hello WenChenHuang

能够简化

 let reduceResult = reduce(array, "Hello ") { $0 + $1}

进一步简化

let reduceResult = reduce(array, "Hello ",+)

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