using System;

using System.Collections.Generic;

using System.Data;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace ConsoleApplication8

{

public static class ListExt

{

public delegate bb MyFunc<in T, out bb>(T arg);

public static List<T> MyWhere<T>(this List<T> list, MyFunc<T,bool> whereLambada )

{

List<T> myList=new List<T>();

foreach (T obj in list)

{

if (whereLambada(obj))

{

myList.Add(obj);

}

}

return myList;

}

}

public class Student

{

public int No { get; set; }

public string Name { get; set; }

public int Age { get; set; }

}

class Program

{

static void Main(string[] args)

{

//TestDb2Entities1 DbContext = new TestDb2Entities1();

//var stu = (from s in DbContext.UserInfoSets where s.Id == 1 select s).First();

//RoleInfoSet r = stu.RoleInfoSets.ToList()[0];

//DataTable table=new DataTable();

//var t = from s in table.AsEnumerable() group s by s.Field<Int32>("") into g select g;

DataTable table = new DataTable();

table.Columns.Add("Id", typeof(Int32));

table.Columns.Add("Name", typeof(String));

table.Columns.Add("Age", typeof(Int32));

DataRow row = table.NewRow();

row["Id"] = 1;

row["Name"] = "1";

row["Age"] = 10;

table.Rows.Add(row);

row = table.NewRow();

row["Id"] = 2;

row["Name"] = "2";

row["Age"] = 2;

table.Rows.Add(row);

row = table.NewRow();

row["Id"] = 1;

row["Name"] = "3";

row["Age"] = 3;

table.Rows.Add(row);

//var stus = from s in table.AsEnumerable() group s by s.Field<Int32>("Id") into g select

//new {

// key=g.Key,value=g

//}

//;

var stus = from s in table.AsEnumerable()

where s.Field<Int32>("Id") == 1

group s by s.Field<Int32>("Id")

into g

select g;

var list = stus.ToList();

var c = list[0].ToList()[1].Field<Int32>("Age");

List<Student> stuList=new List<Student>();

stuList.Add(new Student() { No = 1,Name = "2",Age = 1});

stuList.Add(new Student() {No = 2,Name = "2",Age = 3});

var data = stuList.MyWhere(x => x.No == 1);

Console.ReadKey();

}

}

}