高效的LINQ语句(一)

大家好，欢迎来到IT知识分享网。

Program.cs代码如下:

 class Program { private static void Main(string[] args) { //SelectMany(); //Select_SelectMany_Difference(); //Aggregate(); //How_Long_Entire_Album_Is(); //Expand_Range(); //Expand_Range_In_Order_No_Dups(); Search_Log_Files(); Console.ReadKey(); } public static void SelectMany() { string[] array = { "dot", "net", "perls" }; // 转换 字符数组中的每个字符串 为 单字符数组。 // 然后将这些字符数组合二为一. var result1 = array.SelectMany(element => element.ToCharArray()); // 显示字母 foreach (char letter in result1) { Console.WriteLine(letter); } // 使用像cross join 在 SQL List<int> number = new List<int>() { 10, 20 }; List<string> animals = new List<string>() { "cat", "dog", "donkey" }; List<string> guojia = new List<string>() { "中国", "美国","日本" }; List<string> citys = new List<string>() { "风", "火", "雷", "电", "气", "金", "木","水", "土" }; //摘要: //将序列的每个元素投影到 System.Collections.Generic.IEnumerable<T>，并将结果序列合并为一个序列，并对其中每个元素调用结果选择器函数。 //类型参数: //TSource: source 中的元素的类型。 //TCollection: collectionSelector 收集的中间元素的类型。 //TResult: 结果序列的元素的类型。 //参数: //source: 一个要投影的值序列。 //collectionSelector: 一个应用于输入序列的每个元素的转换函数。 //resultSelector: 一个应用于中间序列的每个元素的转换函数。 var result2 = number.SelectMany(num => animals, (n, a) => new { n, a }); foreach (var resultItem in result2) { Console.WriteLine("{0}{1}", resultItem.n, resultItem.a); } var resultGC = guojia.SelectMany(num => citys, (n, a) => new { n, a }); foreach (var resultItem in resultGC) { Console.WriteLine("{0}{1}", resultItem.n, resultItem.a); } } public static void Select_SelectMany_Difference() { //合并多个集合到一个 Entities[] petOwners = { new Entities {Name = "Higa, Sidney", Pets = new List<string> {"Scruffy", "Sam"}}, new Entities {Name = "Ashkenazi, Ronen", Pets = new List<string> {"Walker", "Sugar"}}, new Entities {Name = "Price, Vernette", Pets = new List<string> {"Scratches", "Diesel"}} }; IEnumerable<List<String>> result1 = petOwners.Select(petOwner => petOwner.Pets); //注意到两个foreach循环都需要通过结果来迭代，因为查询都返回集合。 foreach (List<String> petList in result1) { foreach (string pet in petList) { Console.WriteLine(pet); } } Console.WriteLine("----------------------------------------------------------"); IEnumerable<string> result2 = petOwners.SelectMany(petOwner => petOwner.Pets); // 只有一个foreach循环需要迭代，因为它的结果是一维集合。 foreach (string pet in result2) { Console.WriteLine(pet); } } public static void Aggregate() { int[] array = { 1, 2, 3, 4, 5 }; int result = array.Aggregate((a, b) => b + a); // 1 + 2 = 3 // 3 + 3 = 6 // 6 + 4 = 10 // 10 + 5 = 15 Console.WriteLine(result); int result1 = array.Aggregate((a, b) => b * a); // 1 * 2 = 2 // 2 * 3 = 6 // 6 * 4 = 24 // 24 * 5 = 120 Console.WriteLine(result1); string sentence = "the quick brown fox jumps over the lazy dog"; //拆分字符串为单个单词。 string[] words = sentence.Split(' '); //预先准备每个单词到新句子的开头来扭转词序。 //参数: //source: 要聚合的 System.Collections.Generic.IEnumerable<T>。 //func: 要对每个元素调用的累加器函数。 //返回值: 累加器的最终值。 string result3 = words.Aggregate((workingSentence, next) => next + " " + workingSentence); Console.WriteLine(result3); } public static void How_Long_Entire_Album_Is() { var trackTimes = "2:54,3:48,4:51,3:32,6:15,4:08,5:17,3:13,4:16,3:55,4:53,5:35,4:24"; var totalTrackTimesInSeconds = trackTimes.Split(',') .Select(t => "0:" + t) .Select(t => TimeSpan.Parse(t)) .Select(t => t.TotalSeconds) .Sum(); var totalTrackTimes = TimeSpan.FromSeconds(totalTrackTimesInSeconds); Console.WriteLine(totalTrackTimes); Console.WriteLine(trackTimes.Split(',').Select(t => TimeSpan.Parse("0:" + t)).Aggregate((t1, t2) => t1 + t2)); } public static void Expand_Range() { // 扩大范围 // 例如，“2,3-5,7”应该扩大到2,3,4,5,7 var data = "2,5,7-10,11,17-18"; var result = data .Split(',') .Select(x => x.Split('-')) .Select(p => new { First = int.Parse(p[0]), Last = int.Parse(p.Last()) }) .SelectMany(r => Enumerable.Range(r.First, r.Last - r.First + 1)); Console.WriteLine(result); } public static void Expand_Range_In_Order_No_Dups() { // 扩大范围 // 例如，“2,3-5,7”应该扩大到2,3,4,5,7 // "6,1-3,2-4" 应该扩大到 1,2,3,4,6 var data = "6,1-3,2-4"; var result = data .Split(',') .Select(x => x.Split('-')) .Select(p => new { First = int.Parse(p[0]), Last = int.Parse(p.Last()) }) .SelectMany(r => Enumerable.Range(r.First, r.Last - r.First + 1)) .OrderBy(r => r) .Distinct(); } public static void Search_Log_Files() { //指定用于检索系统特殊文件夹的目录路径的枚举常数。 var myDocs = Environment.GetFolderPath(Environment.SpecialFolder.Desktop); var diagsFolder = Path.Combine(myDocs, "", "tec"); var fileType = "*.txt"; var searchTerm = "JSONArray"; var result = Directory.EnumerateFiles(diagsFolder, fileType).SelectMany(file => File.ReadAllLines(file,Encoding.UTF8) .Select((line, index) => new { File = file, Text = line, LineNumber = index + 1 })).Where(line => Regex.IsMatch(line.Text, searchTerm)); Console.WriteLine(result.FirstOrDefault().Text); } }