如何使用 GroupBy() 通过 VB.NET 对多列进行分组? [英] How to use GroupBy() to group over multiple columns with VB.NET?
问题描述
我尝试像在 C# 中那样使用匿名类型执行此操作,但结果不正确.
i tried to do this like i would in C#, with an anonymous type but the result is just not correct.
VB.NET 示例(错误输出):
VB.NET example (wrong output):
Module Module1
Sub Main()
Dim ls As List(Of Employee) = New List(Of Employee)
ls.Add(New Employee With {.Age = 20, .Sex = "M"})
ls.Add(New Employee With {.Age = 20, .Sex = "M"})
ls.Add(New Employee With {.Age = 20, .Sex = "M"})
ls.Add(New Employee With {.Age = 30, .Sex = "F"})
ls.Add(New Employee With {.Age = 30, .Sex = "F"})
For Each item In ls.GroupBy(Function(k) New With {.Age = k.Age, .Sex = k.Sex})
Console.WriteLine(String.Format("Group [Age: {0}, Sex: {1}] : {2} Item(s)", item.Key.Age, item.Key.Sex, item.Count()))
Next
Console.ReadLine()
End Sub
Class Employee
Private _Age As Integer
Public Property Age() As Integer
Get
Return _Age
End Get
Set(ByVal value As Integer)
_Age = value
End Set
End Property
Private _Sex As String
Public Property Sex() As String
Get
Return _Sex
End Get
Set(ByVal value As String)
_Sex = value
End Set
End Property
End Class
End Module
输出:
Group [Age: 20, Sex: M] : 1 Item(s)
Group [Age: 20, Sex: M] : 1 Item(s)
Group [Age: 20, Sex: M] : 1 Item(s)
Group [Age: 30, Sex: F] : 1 Item(s)
Group [Age: 30, Sex: F] : 1 Item(s)
所需的输出:
Group [Age: 20, Sex: M] : 3 Item(s)
Group [Age: 30, Sex: F] : 2 Item(s)
C# 示例(正确输出):
C# example (correct output):
class Program
{
static void Main(string[] args)
{
List<Employee> ls = new List<Employee>();
ls.Add(new Employee { Age = 20, Sex = "M" });
ls.Add(new Employee { Age = 20, Sex = "M" });
ls.Add(new Employee { Age = 20, Sex = "M" });
ls.Add(new Employee { Age = 30, Sex = "F" });
ls.Add(new Employee { Age = 30, Sex = "F" });
foreach (var item in ls.GroupBy(k => new { Age = k.Age, Sex = k.Sex }))
{
Console.WriteLine(String.Format("Group [Age: {0}, Sex: {1}] : {2} Item(s)", item.Key.Age, item.Key.Sex, item.Count()));
}
Console.ReadLine();
}
class Employee
{
public int Age { get; set; }
public string Sex { get; set; }
}
}
有人看到我的错误在哪里吗?
does anybody see where my error is?
推荐答案
在 VB 代码中创建匿名类型时需要使用 Key
修饰符.默认情况下,它创建读/写属性,而 C# 匿名类型总是只读.Equals
/GetHashCode
中仅使用只读属性.
You need to use the Key
modifier when creating the anonymous types in the VB code. By default it creates read/write properties whereas C# anonymous types are always read-only. Only read-only properties are used in Equals
/ GetHashCode
.
For Each item In ls.GroupBy(Function(k) New With { Key .Age = k.Age, _
Key .Sex = k.Sex})
有关详细信息,请参阅有关 VB 中匿名类型的文档.
See the documentation for anonymous types in VB for more details.
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