static void DeferredQuery() { var names = new List<string> { "Nino", "Alberto", "Juan", "Mike", "Phil" }; var namesWithJ = from n in names where n.StartsWith("J") orderby n select n; Console.WriteLine("First iteration"); foreach (string name in namesWithJ) { Console.WriteLine(name); } Console.WriteLine(); names.Add("John"); names.Add("Jim"); names.Add("Jack"); names.Add("Denny"); Console.WriteLine("Second iteration"); foreach (string name in namesWithJ) { Console.WriteLine(name); } /* First iteration Juan second iteration Jack Jim John Juan */ } //如查询出来自巴西的所有世界冠军,并按照夺冠次数排序 static void LINQQuery() { var query = from r in Formula1.GetChampions() where r.Country == "Brazil" orderby r.Wins descending select r; foreach (var r in query) { Console.WriteLine("{0:A}", r); } } //Zip合并功能 static void ZipOperation() { var racerNames = from r in Formula1.GetChampions() where r.Country == "Italy" orderby r.Wins descending select new { Name = r.FirstName + " " + r.LastName }; var racerNamesAndStarts = from r in Formula1.GetChampions() where r.Country == "Italy" orderby r.Wins descending select new { LastName = r.LastName, Starts = r.Starts }; //var racers = racerNames.Zip(racerNamesAndStarts, (first, second) => first.Name + ", starts: " + second.Starts); //foreach (var r in racers) //{ // Console.WriteLine(r); //} } //根据赛手获得一级方程式冠军的次数,列出最成功的国家 static void Aggregate2() { var countries = (from c in from r in Formula1.GetChampions() group r by r.Country into c select new { Country = c.Key, Wins = (from r1 in c select r1.Wins).Sum() } orderby c.Wins descending, c.Country select c).Take(5); foreach (var country in countries) { Console.WriteLine("{0} {1}", country.Country, country.Wins); } } //筛选赛手,只返回获得冠军次数超过3次的赛手 static void Aggregate() { var query = from r in Formula1.GetChampions() where r.Years.Count() > 3 orderby r.Years.Count() descending select new { Name = r.FirstName + " " + r.LastName, TimesChampion = r.Years.Count() }; foreach (var r in query) { Console.WriteLine("{0} {1}", r.Name, r.TimesChampion); } } //Linq分页显示 static void Partitioning() { int pageSize = 5; int numberPages = (int)Math.Ceiling(Formula1.GetChampions().Count() / (double)pageSize); for (int page = 0; page < numberPages; page++) { Console.WriteLine("Page {0}", page); var racers = (from r in Formula1.GetChampions() orderby r.LastName select r.FirstName + " " + r.LastName). Skip(page * pageSize).Take(pageSize); foreach (var name in racers) { Console.WriteLine(name); } Console.WriteLine(); } } //有驾驶法拉利和迈凯轮的冠军，集合交集 static void SetOperations() { Func<string, IEnumerable<Racer>> racersByCar = car => from r in Formula1.GetChampions() from c in r.Cars where c == car orderby r.LastName select r; Console.WriteLine("World champion with Ferrari and McLaren"); foreach (var racer in racersByCar("Ferrari").Intersect(racersByCar("McLaren"))) { Console.WriteLine(racer); } } //列出每年的赛手冠军和车队冠军 static void Join() { var racers = from r in Formula1.GetChampions() from y in r.Years where y > 2003 select new { Year = y, Name = r.FirstName + " " + r.LastName }; var teams = from t in Formula1.GetContructorChampions() from y in t.Years where y > 2003 select new { Year = y, Name = t.Name }; var racersAndTeams = from r in racers join t in teams on r.Year equals t.Year select new { Year = r.Year, Racer = r.Name, Team = t.Name }; Console.WriteLine("Year Champion " + "Constructor Title"); foreach (var item in racersAndTeams) { Console.WriteLine("{0}: {1,-20} {2}", item.Year, item.Racer, item.Team); } } //现在一级方程式冠军应按照国家分组,并列出一个国家的冠军数以及包含赛手名序列 static void GroupingWithNestedObjects() { var countries = from r in Formula1.GetChampions() group r by r.Country into g orderby g.Count() descending, g.Key where g.Count() >= 2 select new { Country = g.Key, Count = g.Count(), Racers = from r1 in g orderby r1.LastName select r1.FirstName + " " + r1.LastName }; foreach (var item in countries) { Console.WriteLine("{0, -10} {1}", item.Country, item.Count); foreach (var name in item.Racers) { Console.Write("{0}; ", name); } Console.WriteLine(); } } static void Grouping() { var countries = from r in Formula1.GetChampions() group r by r.Country into g orderby g.Count() descending, g.Key where g.Count() >= 2 select new { Country = g.Key, Count = g.Count() }; foreach (var item in countries) { Console.WriteLine("{0, -10} {1}", item.Country, item.Count); } } //显示驾驶法拉利的所有一级方程式冠军名字 static void CompoundFrom() { var ferrariDrivers = from r in Formula1.GetChampions() from c in r.Cars where c == "Ferrari" orderby r.LastName select r.FirstName + " " + r.LastName; foreach (var racer in ferrariDrivers) { Console.WriteLine(racer); } } static void TypeFiltering() { object[] data = { "one", 2, 3, "four", "five", 6 }; var query = data.OfType<string>(); foreach (var s in query) { Console.WriteLine(s); } /* one four five */ } //使用索引返回姓氏以A开头、索引为偶数的赛手 static void IndexFiltering() { var racers = Formula1.GetChampions(). Where((r, index) => r.LastName.StartsWith("A") && index % 2 != 0); foreach (var r in racers) { Console.WriteLine("{0:A}", r); } } //找出赢得至少 15场比赛的巴西和奥地利赛手 static void Filtering() { var racers = from r in Formula1.GetChampions() where r.Wins > 15 && (r.Country == "Brazil" || r.Country == "Austria") select r; foreach (var r in racers) { Console.WriteLine("{0:A}", r); } } //取消Linq并行操作 static void Cancellation() { const int arraySize = 100000000; var data = new int[arraySize]; var r = new Random(); for (int i = 0; i < arraySize; i++) { data[i] = r.Next(40); } var cts = new CancellationTokenSource(); new Thread(() => { try { var sum = (from x in data.AsParallel().WithCancellation(cts.Token) where x < 80 select x).Sum(); Console.WriteLine("query finished, sum: {0}", sum); } catch (OperationCanceledException ex) { Console.WriteLine(ex.Message); } }).Start(); Console.WriteLine("query started"); Console.Write("cancel? "); int input = Console.Read(); if (input == 'Y' || input == 'y') { // cancel! cts.Cancel(); } } //Linq 并行操作 static void IntroParallel() { const int arraySize = 100000000; var data = new int[arraySize]; var r = new Random(); for (int i = 0; i < arraySize; i++) data[i] = r.Next(40); Stopwatch watch = new Stopwatch(); watch.Start(); var q1 = (from x in Partitioner.Create(data).AsParallel() where x < 80 select x).Sum(); watch.Stop(); Console.WriteLine(watch.ElapsedMilliseconds); }
