const string text = @"Historically, the world of data and the world of objects" +

                                 @" have not been well integrated. Programmers work in C# or Visual Basic" +

                                 @" and also in SQL or XQuery. On the one side are concepts such as classes," +

                                 @" objects, fields, inheritance, and .NET Framework APIs. On the other side" +

                                 @" are tables, columns, rows, nodes, and separate languages for dealing with" +

                                 @" them. Data types often require translation between the two worlds; there are" +

                                 @" different standard functions. Because the object world has no notion of query, a" +

                                 @" query can only be represented as a string without compile-time type checking or" +

                                 @" IntelliSense support in the IDE. Transferring data from SQL tables or XML trees to" +

                                 @" objects in memory is often tedious and error-prone.";

             const string searchTerm = "data";

             //字符串转换成数组

             var source = text.Split(new[] { '.', '?', '!', ' ', ';', ':', ',' }, StringSplitOptions.RemoveEmptyEntries);

             //创建查询，并忽略大小写比较

             var matchQuery = from word in source

                              where string.Equals(word, searchTerm, StringComparison.InvariantCultureIgnoreCase)

                              select word;

             //统计匹配数量

             var wordCount = matchQuery.Count();

             Console.WriteLine($"{wordCount} occurrences(s) of the search term \"{searchTerm}\" were found.");

             const string text = @"Historically, the world of data and the world of objects " +

                                 @"have not been well integrated. Programmers work in C# or Visual Basic " +

                                 @"and also in SQL or XQuery. On the one side are concepts such as classes, " +

                                 @"objects, fields, inheritance, and .NET Framework APIs. On the other side " +

                                 @"are tables, columns, rows, nodes, and separate languages for dealing with " +

                                 @"them. Data types often require translation between the two worlds; there are " +

                                 @"different standard functions. Because the object world has no notion of query, a " +

                                 @"query can only be represented as a string without compile-time type checking or " +

                                 @"IntelliSense support in the IDE. Transferring data from SQL tables or XML trees to " +

                                 @"objects in memory is often tedious and error-prone.";

             //将文本块切割成数组

             var sentences = text.Split('.', '?', '!');

             //定义搜索条件，此列表可以运行时动态添加

             string[] wordsToMatch = { "Historically", "data", "integrated" };

             var match = from sentence in sentences

                         let t =

                             sentence.Split(new char[] { '.', '?', '!', ' ', ';', ':', ',' }, StringSplitOptions.RemoveEmptyEntries)

                         where t.Distinct().Intersect(wordsToMatch).Count() == wordsToMatch.Length   //去重，取交集后的数量对比

                         select sentence;

             foreach (var s in match)

             {

                 Console.WriteLine(s);

             }

             const string aString = "ABCDE99F-J74-12-89A";

             //只选择数字的字符

             var digits = from ch in aString

                          where char.IsDigit(ch)

                          select ch;

             Console.Write("digit: ");

             foreach (var n in digits)

             {

                 Console.Write($"{n} ");

             }

             Console.WriteLine();

             //选择第一个“-”之前的所有字符

             var query = aString.TakeWhile(x => x != '-');

             foreach (var ch in query)

             {

                 Console.Write(ch);

             }

             //根据不同版本的 vs 修改路径

             const string floder = @"C:\Program Files (x86)\Microsoft Visual Studio 14.0\";

             var infoes = GetFiles(floder);

             //创建正则表达式来寻找所有的"Visual"

             var searchTerm = new Regex(@"Visual (Basic|C#|C\+\+|J#|SourceSafe|Studio)");

             //搜索每一个“.html”文件

             //通过 where 找到匹配项

             //【注意】select 中的变量要求显示声明其类型，因为 MatchCollection 不是泛型 IEnumerable 集合

             var query = from fileInfo in infoes

                         where fileInfo.Extension == ".html"

                         let text = File.ReadAllText(fileInfo.FullName)

                         let matches = searchTerm.Matches(text)

                         where matches.Count >

                         select new

                         {

                             name = fileInfo.FullName,

                             matchValue = from Match match in matches select match.Value

                         };

             Console.WriteLine($"The term \"{searchTerm}\" was found in:");

             foreach (var q in query)

             {

                 //修剪匹配找到的文件中的路径

                 Console.WriteLine($"{q.name.Substring(floder.Length - 1)}");

                 //输出找到的匹配值

                 foreach (var v in q.matchValue)

                 {

                     Console.WriteLine(v);

                 }

             }

         private static IList<FileInfo> GetFiles(string path)

         {

             var files = Directory.GetFiles(path, "*.*", SearchOption.AllDirectories);

             return files.Select(file => new FileInfo(file)).ToList();

         }