LINQ Group by 多列值在C#与VB.Net上写法的区别

现有这样一个LIST，需要根据Age和Sex两列进行Group by 分组操作：

 

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# 很好实现，一般这样来写LINQ语句：

// 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()};

 

现在需要用VB.Net来实现，根据上边C#的写法，很容易想到这样来写：

' 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()}

 

但是打印一下结果发现不对，后来仔细研究了下，原来问题出在这:

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

 

换成这样，结果就和C#的一样了:

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

 

看来在VB.NET中，匿名类和C#不一样，当Group by多列时，需要全部指定它们为Key，不然不会将它们作为一个整体进行group by

 

以下是全部代码:
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代码:

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

 

 

相关讲讨论讨论帖子:

 

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