The difference between writing a multi-column value in a LINQ group by statement in C # and VB. NET

If such a list exists, you need to perform group by operation based on the age and sex columns:

 

 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'}  };

C # Is a good implementation. Generally, write the LINQ statement as follows:

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

 

Now we need to use VB. NET to implement it. According to the above C # statement, it is easy to think of writing like this:

' query with lamdaexpressionDim 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 expressionDim 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()} 

 

However, the printed results showed that they were incorrect. After careful research, the original problem was as follows:

Group El by key = new with {El. Age, El. Sex} into G = group _

 

In this case, the result is the same as that of C:

Group El by key = new with {key El. Age, key El. Sex} into G = group _

 

It seems that in VB. NET, anonymous classes are different from C #. When group by has multiple columns, you must specify all of them as keys. Otherwise, they will not be grouped by as a whole.

 

All the code is as follows:
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 lamdaexpressionvar QueryWithLamda = empList.GroupBy(x => new { x.Age,  x.Sex})            .Select(g=>new {g.Key, Count=g.Count()}); //query with standard expressionvar 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 code:

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 lamdaexpressionDim 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 expressionDim 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 SubPublic Class Employee Private privateID As IntegerPublic Property ID() As Integer Get Return privateIDEnd Get Set(ByVal value As Integer) privateID = valueEnd Set End Property Private privateFName As String Public Property FName() As StringGet Return privateFNameEnd Get Set(ByVal value As String) privateFName = valueEnd Set End Property  Private privateAge As Integer Public Property Age() As IntegerGet Return privateAgeEnd Get Set(ByVal value As Integer) privateAge = valueEnd Set End Property  Private privateSex As Char Public Property Sex() As CharGet Return privateSexEnd Get Set(ByVal value As Char) privateSex = valueEnd Set End PropertyEnd Class 

 

 

Related discussion posts:

 

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