C#中Linq的入门教程

int[] arr = new int[] { 1, 4, 2, 6, 7, 9, 5, 1, 2, 4 };
var query = from r in arr
            where r < 5
            orderby r
            select r;
foreach (var item in query)
{
    Console.WriteLine(item);
}
Console.ReadLine();

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);
}

var namesWithJ = (from n in names
                  where n.StartsWith("J")
                  orderby n
                  select n
).ToList();

var nuMQuery2 =
           (from num in numbers
            where (num % 2) == 0
            select num).ToList();
var numQuery3 =
          (from num in numbers
           where (num % 2) == 0
            select num).ToArray();

class Student
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string City { get; set; }
    public List<int> Scores { get; set; }
}

class Teacher
{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public string City { get; set; }
}

private static void Main(string[] args)
{
    //创建第一个数据源
    var students = new List<Student>() {
            new Student () {
            Age = 23,
            City = "广州",
            Name = "小C",
            Scores = new List<int> () { 85, 88, 83, 97 }
            },
            new Student () {
            Age = 18,
            City = "广西",
            Name = "小明",
            Scores = new List<int> () { 86, 78, 85, 90 }
            },
            new Student () {
            Age = 33,
            City = "梦里",
            Name = "小叁",
            Scores = new List<int> () { 86, 68, 73, 97 }
            }
        };

    //创建第二个数据源
    var teachers = new List<Teacher>() {
            new Teacher () {
            Age = 35,
            City = "梦里",
            Name = "啵哆"
            },
            new Teacher () {
            Age = 28,
            City = "云南",
            Name = "小红"
            },
            new Teacher () {
            Age = 38,
            City = "河南",
            Name = "丽丽"
            }
        };

    //创建查询
    var peopleInDreams = (from student in students
                          where student.City == "梦里"
                          select student.Name)
                .Concat(from teacher in teachers
                        where teacher.City == "梦里"
                        select teacher.Name);

    //执行查询
    foreach (var person in peopleInDreams)
    {
        Console.WriteLine(person);
    }

    Console.Read();
}

var query = from cust in Customers
               select cust.City;

var query = from cust in Customer
               select new {Name = cust.Name, City = cust.City};

//创建数据源
var students = new List<Student>()
            {
                new Student()
                {
                    Age = 18,
                    Name = "小A",
                    Scores = new List<int>() {88,85,74,66 }
                },
                new Student()
                {
                    Age = 35,
                    Name = "小B",
                    Scores = new List<int>() {88,85,74,66 }
                },
                new Student()
                {
                    Age = 28,
                    Name = "小啥",
                    Scores = new List<int>() {88,85,74,66 }
                }
            };

//创建查询
var studentsToXml = new XElement("Root",
    from student in students
    let x = $"{student.Scores[0]},{student.Scores[1]},{student.Scores[2]},{student.Scores[3]}"
    select new XElement("student",
           new XElement("Name", student.Name),
           new XElement("Age", student.Age),
           new XElement("Scores", x))
);

//执行查询
Console.WriteLine(studentsToXml);

//数据源
double[] radii = { 1, 2, 3 };

//创建查询
var query = from radius in radii
            select $"{radius * radius * 3.14}";

//执行查询
foreach (var i in query)
{
    Console.WriteLine(i);
}