Group By 的用法

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;
using System.IO;

namespace Csharp
{
    class Program
    {
        class GroupSample1
        {
            // The element type of the data source.
            public class Student
            {
                public string First { get; set; }
                public string Last { get; set; }
                public int ID { get; set; }
                public List
   
   
    
     Scores;
            }

            public static List
    
    
     
      GetStudents()
            {
                // Use a collection initializer to create the data source. Note that each element
                //  in the list contains an inner sequence of scores.
                List
     
     
      
       students = new List
      
      
       
       
        {
           new Student {First="Svetlana", Last="Omelchenko", ID=111, Scores= new List
       
       
         {97, 72, 81, 60}}, new Student {First="Claire", Last="O'Donnell", ID=112, Scores= new List 
        
          {75, 84, 91, 39}}, new Student {First="Sven", Last="Mortensen", ID=113, Scores= new List 
         
           {99, 89, 91, 95}}, new Student {First="Cesar", Last="Garcia", ID=114, Scores= new List 
          
            {72, 81, 65, 84}}, new Student {First="Debra", Last="Garcia", ID=115, Scores= new List 
           
             {97, 89, 85, 82}} }; return students; } static void Main(string[] args) { var students = GetStudents(); //group by pass or fail var boolQuery = from student in students group student by student.Scores.Average() > 80; foreach (var studentGroup in boolQuery) { Console.WriteLine((studentGroup.Key == true) ? "High Averages" : "Low Averages"); foreach (var student in studentGroup) Console.WriteLine("{0} {1}'s average score is {2}", student.First, student.Last, student.Scores.Average()); } Console.WriteLine("-------------------------------------"); //group by the score rank var groupByScoresQuery = from student in students let avg = (int)student.Scores.Average() group student by (avg == 0 ? 0 : avg / 10) into g orderby g.Key select g; foreach (var studentGroup in groupByScoresQuery) { var avgLowBound = studentGroup.Key * 10; Console.WriteLine("the students' scores between the {0} to {1}", avgLowBound, avgLowBound + 10); foreach (var student in studentGroup) Console.WriteLine("{0} {1}'s average score is {2}", student.First, student.Last, student.Scores.Average()); } } } } }