swift 函数编程

读入一个文本，确定所有单词的使用频率并从高到底排序，打印出所有单词以及其频率列表

先不解决频率问题 先看下不使用高阶函数

//: A UIKit based Playground for presenting user interface

import UIKit


//去掉一些语气次 不加入计算
let NON_WORDS:Set = ["the","and","of","to","a","i","it","in","or","is","as","so","but","be"]
//传统解决方法
func wordFreq(words:String)->[String:Int]{
    var wordDict:[String:Int]=[:]
    let wordList=words.split(separator: " ")
    for word in wordList{
        let lowerCaseWord=word.lowercased()
        if !NON_WORDS.contains(lowerCaseWord){
            if let count = wordDict[lowerCaseWord]{
                wordDict[lowerCaseWord] = count+1
            }else{
                wordDict[lowerCaseWord]=1
            }
        }
    }
    return wordDict;
}

let words="""
There are moments in life when you miss someone so much that you just want to pick them from your dreams and hug them for real!
"""
print(wordFreq(words: words))

["there": 1, "pick": 1, "them": 2, "your": 1, "for": 1, "dreams": 1, "hug": 1, "when": 1, "real!": 1, "that": 1, "you": 2, "are": 1, "life": 1, "miss": 1, "just": 1, "moments": 1, "from": 1, "much": 1, "want": 1, "someone": 1]

使用高级函数

//: A UIKit based Playground for presenting user interface

import UIKit


//去掉一些语气次 不加入计算
let NON_WORDS:Set = ["the","and","of","to","a","i","it","in","or","is","as","so","but","be"]
//函数编程
func wordFreq(words:String)->[String:Int]{
    var wordDict:[String:Int]=[:]
    let wordList=words.split(separator: " ")
    wordList.map {$0.lowercased()}
        .filter{ !NON_WORDS.contains($0)}
        .forEach{(word) in
            wordDict[word]=(wordDict[word] ?? 0)+1
    }
    return wordDict;
}

let words="""
There are moments in life when you miss someone so much that you just want to pick them from your dreams and hug them for real!
"""
print(wordFreq(words: words))

排序很简单

  wordDict.sorted {$0.1 > $1.1}

 业务需求

假设我们有一个名字列表，其中一些条目由单个字符构成。现在的任务是，将出去单字符之外的列表内容，放在一个逗号分割的字符串里返回，且每个名字的首字母都要大写

命令式解法

传统for循环：

//: A UIKit based Playground for presenting user interface

import UIKit
let emlpyee = ["neal","s","stu","j","rich","bob","aiden","j","ethan"]

func cleanNamaes(names:Array<String>)->String{
    var clearnedNames = ""
    for name in names{
        if name.count>1{
            clearnedNames += name.capitalized + ","
        }
        
    }
    clearnedNames.remove(at: clearnedNames.index(before: clearnedNames.endIndex))
    return clearnedNames
}
let res=cleanNamaes(names: emlpyee)
print(res)

高阶函数

let res2=emlpyee.filter{ $0.count>1 }
    .map{ $0.capitalized }
.joined(separator: ",")

结果

Neal,Stu,Rich,Bob,Aiden,Ethan