高效的LINQ语句(一)

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, "QQ", "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);        }             }