現有這樣一個LIST,需要根據Age和Sex兩列進行Group by 分組操作:

	 var  empList =new List<Employee>
	 {
		new Employee {ID = 1, FName = "John", Age = 23, Sex = 'M'},
		new Employee {ID = 2, FName = "Mary", Age = 25, Sex = 'F'},
		new Employee {ID = 3, FName = "Amber", Age = 23, Sex = 'M'},
		new Employee {ID = 4, FName = "Kathy", Age = 25, Sex = 'F'},
		new Employee {ID = 5, FName = "Lena", Age = 27, Sex = 'F'},
		new Employee {ID = 6, FName = "Bill", Age = 28, Sex = 'M'},
		new Employee {ID = 7, FName = "Celina", Age = 27, Sex = 'F'},
		new Employee {ID = 8, FName = "John", Age = 28, Sex = 'M'} 
	 };

用C# 很好實現,一般這樣來寫LINQ語句:

	// query with lamda	expression
	var QueryWithLamda = empList.GroupBy(x => new { x.Age,  x.Sex})
	            .Select(g=>new {g.Key, Count=g.Count()}); 
	
	//query with standard expression
	var query=from el in empList
	          group el by new {el.Age,el.Sex} into g
			  select new {g.Key, Count=g.Count()}; 

現在需要用VB.Net來實現,根據上邊C#的寫法,很容易想到這樣來寫:

	' query with lamda	expression	
	Dim QueryWithLamda =  empList.GroupBy(Function(x)  New With { .Age=x.Age, .Sex= x.Sex}) _ 
								 .Select(Function(g) New With {g.Key, g.Count()})  

	
	' query with standard expression
	Dim Query = From el In empList _ 
			    Group el By Key = new with { el.Age,  el.Sex} Into g= Group  _ 
			    Select New  With {.key = Key, _
								.count = g.Count()} 

但是列印一下結果發現不對,後來仔細研究了下,原來問題出在這:

Group el By Key = new with {el.Age, el.Sex} Into g= Group _

換成這樣,結果就和C#的一樣了:

Group el By Key = new with{key el.Age, key el.Sex} Into g= Group  _

看來在VB.NET中,匿名類和C#不一樣,當Group by多列時,需要全部指定它們為Key,不然不會將它們作為一個整體進行group by

以下是全部程式碼:
C#:

void Main()
{
	 var  empList =new List<Employee>
	 {
		new Employee {ID = 1, FName = "John", Age = 23, Sex = 'M'},
		new Employee {ID = 2, FName = "Mary", Age = 25, Sex = 'F'},
		new Employee {ID = 3, FName = "Amber", Age = 23, Sex = 'M'},
		new Employee {ID = 4, FName = "Kathy", Age = 25, Sex = 'F'},
		new Employee {ID = 5, FName = "Lena", Age = 27, Sex = 'F'},
		new Employee {ID = 6, FName = "Bill", Age = 28, Sex = 'M'},
		new Employee {ID = 7, FName = "Celina", Age = 27, Sex = 'F'},
		new Employee {ID = 8, FName = "John", Age = 28, Sex = 'M'} 
	 };
		
	// query with lamda	expression
	var QueryWithLamda = empList.GroupBy(x => new { x.Age,  x.Sex})
	            .Select(g=>new {g.Key, Count=g.Count()}); 
	
	//query with standard expression
	var query=from el in empList
	          group el by new {el.Age,el.Sex} into g
			  select new {g.Key, Count=g.Count()}; 
 
	foreach (var employee in query /* Or  QueryWithLamda */ )
			 Console.WriteLine(employee.Count);
	 
}

public class Employee
{
  public int ID {get;set;}
  public string FName {get;set;}
  public int Age {get;set;}
  public char Sex {get;set;}
}

VB.NET程式碼:

Sub Main
	 Dim empList As New List(Of Employee)()
		empList.Add(New Employee() With _
		{.ID = 1, .FName = "John", .Age = 23, .Sex = "M"c}) 
		empList.Add(New Employee() With _
		{.ID = 2, .FName = "Mary", .Age = 25, .Sex = "F"c})
		empList.Add(New Employee() With _
		{.ID = 3, .FName = "Amber", .Age = 23, .Sex = "M"c}) 
		empList.Add(New Employee() With _
		{.ID = 4, .FName = "Kathy", .Age = 25, .Sex = "F"c})
		empList.Add(New Employee() With _
		{.ID = 5, .FName = "Lena", .Age = 27, .Sex = "F"c}) 
		empList.Add(New Employee() With _
		{.ID = 6, .FName = "Bill", .Age = 28, .Sex = "M"c})
		empList.Add(New Employee() With _
		{.ID = 7, .FName = "Celina", .Age = 27, .Sex = "F"c}) 
		empList.Add(New Employee() With _
		{.ID = 8, .FName = "John", .Age = 28, .Sex = "M"c})
		
	' query with lamda	expression	
	Dim QueryWithLamda = empList.GroupBy(Function(x)  New With { Key x.Age, Key x.Sex}) _
	            				.Select(Function(g) New With {g.Key, g.Count()}) 
	
	' query with standard expression
	Dim QueryWithStanard = From el In empList _ 
			    Group el By Key = new with {Key el.Age, Key el.Sex} Into g= Group  _ 
			    Select New  With {.key = Key, _
								.count = g.Count()} 
								
	Dim QueryWithStanard2 = From el In empList _ 
			    Group el By Key = el.Age,  el.Sex  Into g= Group  _ 
			    Select New  With {.key = Key, _
								.count = g.Count()} 							
 
	For Each employee In QueryWithLamda  'Or  QueryWithLamda
			 Console.WriteLine(employee.Count)
	Next employee 

End Sub
Public Class Employee 
		Private privateID As Integer
		Public Property ID() As Integer 

			Get 
				Return privateID
			End Get 

			Set(ByVal value As Integer) 
				privateID = value
			End Set 

		End Property 

		Private privateFName As String 
		Public Property FName() As String
			Get 
				Return privateFName
			End Get 

			Set(ByVal value As String) 
				privateFName = value
			End Set 
		End Property  

		Private privateAge As Integer 
		Public Property Age() As Integer
			Get 
				Return privateAge
			End Get 

			Set(ByVal value As Integer) 
				privateAge = value
			End Set 
		End Property  

		Private privateSex As Char 
		Public Property Sex() As Char
			Get 
				Return privateSex
			End Get 

			Set(ByVal value As Char) 
				privateSex = value
			End Set 
		End Property
End Class 

相關講討論討論帖子:

http://topic.csdn.net/u/20120529/16/2648950b-26b4-4b90-aa9a-05dff88c85f4.html

http://stackoverflow.com/questions/10801859/linq-group-by-multiple-values-does-not-work-well-in-vb-net-but-work-well-in-c-sh

http://social.microsoft.com/Forums/zh-CN/adonetzhchs/thread/7f06ff9e-a704-411e-9220-7a86963a290e