LINQ基础之From和GroupBy子句

var queryAllCustomers =
        from cust in Customers
        select cust;

//数据源
 IList<Student> students = new List<Student>
{
    new Student{ Name="Kevin", Score=new List<int>{89,93,88,78}},
    new Student{ Name="Jackie",Score=new List<int>{92,87,83,91}},
    new Student{ Name="Helen",Score=new List<int>{53,76,72,62}}
};
            //所有的Linq查询操作都由以下三个不同的操作组成：
            //1.获得数据源
            //2.创建查询
            //3.执行查询

            //使用复合from子句查询命令
            var getStudent =
                    from student in students
                    from score in student.Score
                    where score > 90
                    select new { Name = student.Name, Score = score };

            foreach (var st in getStudent)
            {
                Console.WriteLine("NAME:{0},SCORE:{1}",st.Name,st.Score);
            }

//数据源
string[] fruits = { "apple", "banana", "peach", "orange", "melon", "lemon" };

//分组查询的查询语句
var query = from f in fruits
            group f by f[0];

//执行查询
foreach (var letters in query)
{
    Console.WriteLine("words that start with letter:" + letters.Key);
    foreach (var word in letters)
    {
        Console.WriteLine(word);
    }
}

var query = from f in fruits
             group f by f[0] into g
             where g.Key == 'p' || g.Key == 'b'
             select g;

string[] strs = { "胡广成", "张国荣", "刘德华", "故国冰封", "万里雪飘", "AAA", "胡翰轩", "张杰" };
            var list5 = strs
                //.Where(a => a.Length == 3)
                .Select(item => item)
                .GroupBy(item => item.Length);//分组   分组依据是字符串的长度
            foreach (var item in list5)
            {
                Console.WriteLine("----------------");
                Console.WriteLine($"分组字段是{item.Key}");  //item.Key是分组依据 显示分组字段
                foreach (var items in item)//内层循环遍历分组项
                {
                    Console.WriteLine(items);
                }
            }

GroupBy(x => new { x.a , x.b, x.c }).Select( x=> ( new Class名 { a=x.Key.a , b=x.Key.b , c = x.Key.c } ))