LINQ 操作符

using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;
namespace LinQ
{
    class Program
    {
        static void Main(string[] args)
        {
            l1();
            Console.WriteLine();
            l2();
            Console.WriteLine();
            l3();
            Console.WriteLine();
            l4();
            Console.WriteLine();
            l5();
            Console.WriteLine();
            l6();
            Console.WriteLine();
            l7();
            Console.WriteLine();
            l8();
            Console.WriteLine();
            l9();
            Console.WriteLine();
            l10();
            Console.Read();
        }
        public static void l1()
        {
            int[] scores = new int[] { , , , , , , ,  };
            IEnumerable<int> scoreQuery = from scrore in scores where scrore >  select scrore;
            foreach (int i in scoreQuery)
            {
                Console.Write(i + " ");

            }
        }

        /*linq检索数据转换数据
        *合并两个序列
        */
        class Student
        {
            public string StuNo { get; set; }
            public string StuName { get; set; }
            public string StuCollege { get; set; }
            public List<int> StuScores;
        }
        class Teacher
        {
            public string TeaNo { get; set; }
            public string TeaName { get; set; }
            public string TeaCollege { get; set; }
        }
        public static void l2()
        {
            List<Student> students = new List<Student>() {
            new Student{StuNo ="",StuName ="张三",StuCollege ="信息工程学院",StuScores =new List<int> {,,,}},
            new Student {StuNo ="",StuName ="李四",StuCollege ="机电学院",StuScores =new List<int> {,,,}}
            };
            List<Teacher> teachers = new List<Teacher>() {
            new Teacher {TeaNo ="",TeaName ="张华",TeaCollege ="信息工程学院"},
            new Teacher {TeaNo ="",TeaName ="王丽",TeaCollege ="机电学院"}
            };
            var a = (from student in students where student.StuCollege == "信息工程学院" select student.StuName).Concat(from teacher in teachers
                                                                                                                  where teacher.TeaCollege == "信息工程学院"
                                                                                                                  select teacher.TeaName);
            Console.WriteLine("信息工程学院的老师和同学们有：");
            foreach (var person in a)
            {
                Console.WriteLine(person);
            }
        }
        /*
        *选择源序列元素的一个或多个属性构成元素
        */
        public static void l3()
        {
            List<Student> students = new List<Student>() {
            new Student {StuNo ="",StuName ="张三",StuCollege ="信息工程学院",StuScores=new List<int> {,,,}},
            new Student {StuNo ="",StuName ="李四",StuCollege ="机电学院",StuScores =new List<int> {,,,}}
            };
            var a = from student in students select student.StuName;
            foreach (var person in a)
            {
                Console.WriteLine(person);
            }
            var a1 = from student in students select new { student.StuNo, student.StuName };
            foreach (var person in a1)
            {
                Console.WriteLine("{0},{1}", person.StuNo, person.StuName);
            }
        }

        /*
        * LINQ的推迟查询
        * **/
        public static void l4()
        {
            List<string> Cites = new List<string> { "shanghai", "beijing", "xiamen", "qingdao", "xian" };
            var cityWiths = from c in Cites where c.StartsWith("s") orderby c select c;
            Console.WriteLine("第一次查询名称以‘S’起始的城市");
            foreach (string city in cityWiths)
            {
                Console.WriteLine(city);
            }
            Console.WriteLine();
            Cites.Add("shengzhen");
            Cites.Add("shenyang");
            Console.WriteLine("第二次查询名称以‘s’起始的城市");
            foreach (string city in cityWiths)
            {
                Console.WriteLine(city);
            }
        }

        /*
        * 标准查询操作符
        * where 过滤操作符定义了返回元素的条件
        * select 投射操作符用于把对象转换成另一个类型的对象
        * orderby 排序操作符改变返回元素的顺序
        * group by 组合运算符数据放在一个数组中
        * Count，Sum，Min，Max，Average 合计操作符计算集合的一个值，利用这些合作操作符，可以计算所有值的总和，元素的个数，值最大和最小的元素，平均值
        * Distinct 从集合中删除重复的元素
        * join 链接运算符用于链接两个集合
        * **/

        /*
        * where 子句
        * **/
        public static void l5()
        {
            List<Student> students = new List<Student>() {
            new Student {StuNo ="",StuName ="张三",StuCollege ="信息工程学院",StuScores =new List<int> {,,,}},
            new Student {StuNo="",StuName ="李四",StuCollege ="机电学院",StuScores =new List<int> {,,,}}
            };
            var a = (from student in students
                     where student.StuCollege == "信息工程学院" && student.StuScores.Average() >
                     select student.StuName);
            foreach (var person in a)
            {
                Console.WriteLine(person);
            }
        }
        /*
        * orderby子句
        * **/
        public static void l6()
        {
            List<Student> students = new List<Student>() {
            new Student {StuNo ="",StuName ="张三",StuCollege ="信息工程学院",StuScores =new List<int> {,,,}},
            new Student {StuNo="",StuName ="李四",StuCollege ="机电学院",StuScores =new List<int> {,,,}}
            };
            var a = from student in students orderby student.StuName descending select student.StuName;
            foreach (var person in a)
            {
                Console.WriteLine(person);
            }
        }
        /*
        * group by子句
        * **/
        public static void l7()
        {
            List<Student> students = new List<Student>() {
            new Student {StuNo ="",StuName ="张三",StuCollege ="信息工程学院",StuScores =new List<int> {,,,}},
            new Student {StuNo="",StuName ="李四",StuCollege ="机电学院",StuScores =new List<int> {,,,}},
            new Student {StuNo ="",StuName ="王五",StuCollege ="机电学院",StuScores =new List<int> {,,,}}
            };
            var a = from student in students
                    group student by student.StuCollege into collegeGroup
                    select new { College = collegeGroup.Key, Count = collegeGroup.Count() };
            foreach (var person in a)
            {
                Console.WriteLine("{0}{1}", person.College, person.Count);
            }
        }
        /*
        * 合计操作符
        **/
        public static void l8()
        {
            List<Student> students = new List<Student>() {
            new Student {StuNo ="",StuName ="张三",StuCollege ="信息工程学院",StuScores =new List<int> {,,,}},
            new Student {StuNo="",StuName ="李四",StuCollege ="机电学院",StuScores =new List<int> {,,,}},
            new Student {StuNo ="",StuName ="王五",StuCollege ="机电学院",StuScores =new List<int> {,,,}}
            };
            int a = (from student in students select students).Count();
            //Sum，Min，Max，Average原理与其相同
            Console.WriteLine("学生总数为：");
            Console.WriteLine(a);

        }
        /*
        * Distinct运算符
        *
        **/
        public static void l9()
        {
            List<Student> students = new List<Student>() {
            new Student {StuNo ="",StuName ="张三",StuCollege ="信息工程学院",StuScores =new List<int> {,,,}},
            new Student {StuNo="",StuName ="李四",StuCollege ="机电学院",StuScores =new List<int> {,,,}},
            new Student {StuNo ="",StuName ="王五",StuCollege ="机电学院",StuScores =new List<int> {,,,}}
            };
            var a = (from student in students select student.StuCollege).Distinct();
            foreach (var college in a)
            {
                Console.WriteLine(college);
            }
        }

        /*
        * join用于链接两个集合查询语法为join...in...on....equals
        *
        **/
        class Student3
        {
            public string StuNo { get; set; }
            public string StuName { get; set; }
            public string CollegeNo { get; set; }
            public List<int> StuScores;
        }
        class College
        {
            public string CollegeNo { get; set; }
            public string CollegeName { get; set; }
        }
        public static void l10()
        {
            List<Student3> students = new List<Student3>() {
            new Student3 {StuNo ="",StuName ="张三",CollegeNo ="",StuScores =new List<int> {,,,}},
            new Student3 {StuNo="",StuName ="李四",CollegeNo ="",StuScores =new List<int> {,,,}},
            new Student3 {StuNo ="",StuName ="王五",CollegeNo ="",StuScores =new List<int> {,,,}}
            };
                        List<College> colleges = new List<College>() {
            new College {CollegeNo="",CollegeName ="信息工程学院" },
            new College {CollegeNo ="",CollegeName ="机电学院"}
            };
            var a = from student in students
                    join college in colleges on student.CollegeNo equals college.CollegeNo
                    select new { student.StuName, college.CollegeName };
            foreach (var person in a)
            {
                Console.WriteLine("{0 } {1}", person.StuName, person.CollegeName);
            }

        }
    }
}