Queryable.GroupBy<TSource, TKey, TResult> Method (IQueryable<TSource>, Expression<Func<TSource, TKey>>, Expression<Func<TKey, IEnumerable<TSource>, TResult>>)

Type Parameters

• TSource
  The type of the elements of source.

• TKey
  The type of the key returned by the function represented in keySelector.

• TResult
  The type of the result value returned by resultSelector.

Parameters

• source
  Type: System.Linq.IQueryable<TSource>
  An IQueryable<T> whose elements to group.

• keySelector
  Type: System.Linq.Expressions.Expression<Func<TSource, TKey>>
  A function to extract the key for each element.

• resultSelector
  Type: System.Linq.Expressions.Expression<Func<TKey, IEnumerable<TSource>, TResult>>
  A function to create a result value from each group.

Return Value

Type: System.Linq.IQueryable<TResult>
An T:System.Linq.IQueryable`1 that has a type argument of TResult and where each element represents a projection over a group and its key.

Structure Pet
   Public Name As String
   Public Age As Double
End Structure

Shared Sub GroupByEx3()
   ' Create a list of pets.
   Dim petsList As New List(Of Pet)(New Pet() { _
                      New Pet With {.Name = "Barley", .Age = 8.3}, _
                      New Pet With {.Name = "Boots", .Age = 4.9}, _
                      New Pet With {.Name = "Whiskers", .Age = 1.5}, _
                      New Pet With {.Name = "Daisy", .Age = 4.3}})

   ' Group Pet objects by the Math.Floor of their age.
   ' Then project an anonymous type from each group
   ' that consists of the key, the count of the group's
   ' elements, and the minimum and maximum age in the group.
   Dim query = petsList.AsQueryable().GroupBy( _
       Function(pet) Math.Floor(pet.Age), _
       Function(age, pets) New With { _
           .Key = age, _
           .Count = pets.Count(), _
           .Min = pets.Min(Function(pet) pet.Age), _
           .Max = pets.Max(Function(pet) pet.Age) _
       })

   Dim output As New System.Text.StringBuilder
   ' Iterate over each anonymous type.
   For Each result In query
      output.AppendLine(vbCrLf & "Age group: " & result.Key)
      output.AppendLine("Number of pets with this age: " & result.Count)
      output.AppendLine("Minimum age: " & result.Min)
      output.AppendLine("Maximum age: " & result.Max)
   Next

   ' Display the output.
   outputBlock.Text &= output.ToString() & vbCrLf

   ' This code produces the following output:

   '  Age group: 8
   '  Number of pets with this age: 1
   '  Minimum age: 8.3
   '  Maximum age: 8.3

   '  Age group: 4
   '  Number of pets with this age: 2
   '  Minimum age: 4.3
   '  Maximum age: 4.9

   '  Age group: 1
   '  Number of pets with this age: 1
   '  Minimum age: 1.5
   '  Maximum age: 1.5
End Sub

class Pet
{
   public string Name { get; set; }
   public double Age { get; set; }
}

public static void GroupByEx3()
{
   // Create a list of pets.
   List<Pet> petsList =
       new List<Pet>{ new Pet { Name="Barley", Age=8.3 },
                          new Pet { Name="Boots", Age=4.9 },
                          new Pet { Name="Whiskers", Age=1.5 },
                          new Pet { Name="Daisy", Age=4.3 } };

   // Group Pet objects by the Math.Floor of their age.
   // Then project an anonymous type from each group
   // that consists of the key, the count of the group's
   // elements, and the minimum and maximum age in the group.
   var query = petsList.AsQueryable().GroupBy(
       pet => Math.Floor(pet.Age),
       (age, pets) => new
       {
          Key = age,
          Count = pets.Count(),
          Min = pets.Min(pet => pet.Age),
          Max = pets.Max(pet => pet.Age)
       });

   // Iterate over each anonymous type.
   foreach (var result in query)
   {
      outputBlock.Text += "\nAge group: " + result.Key + "\n";
      outputBlock.Text += "Number of pets in this age group: " + result.Count + "\n";
      outputBlock.Text += "Minimum age: " + result.Min + "\n";
      outputBlock.Text += "Maximum age: " + result.Max + "\n";
   }

   /*  This code produces the following output:

       Age group: 8
       Number of pets in this age group: 1
       Minimum age: 8.3
       Maximum age: 8.3

       Age group: 4
       Number of pets in this age group: 2
       Minimum age: 4.3
       Maximum age: 4.9

       Age group: 1
       Number of pets in this age group: 1
       Minimum age: 1.5
       Maximum age: 1.5
   */
}