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MSDN Library

IGrouping(Of TKey, TElement).Key Property

Gets the key of the IGrouping(Of TKey, TElement).

Namespace:  System.Linq
Assemblies:   System.Linq (in System.Linq.dll)
  System.Core (in System.Core.dll)

'Declaration
ReadOnly Property Key As TKey

Property Value

Type: TKey
The key of the IGrouping(Of TKey, TElement).

The key of an IGrouping(Of TKey, TElement) represents the attribute that is common to each value in the IGrouping(Of TKey, TElement).

The following example demonstrates how to use the Key property to label each IGrouping(Of TKey, TElement) object in a sequence of IGrouping(Of TKey, TElement) objects. The GroupBy(Of TSource, TKey)(IEnumerable(Of TSource), Func(Of TSource, TKey)) method is used to obtain a sequence of IGrouping(Of TKey, TElement) objects. The foreach in Visual C# or For Each in Visual Basic loop then iterates through each IGrouping(Of TKey, TElement) object, outputting its key and the number of values it contains.

        ' Get a sequence of IGrouping objects. 
        Dim memberQuery As  _
        IEnumerable(Of IGrouping(Of System.Reflection.MemberTypes, System.Reflection.MemberInfo)) = _
            Type.GetType("String").GetMembers(). _
            GroupBy(Function(ByVal member) member.MemberType)

        ' Output the key of each IGrouping object and the count of values. 
        For Each group As  _
        IGrouping(Of System.Reflection.MemberTypes, System.Reflection.MemberInfo) In memberQuery
            MsgBox(String.Format("(Key) {0} (Member count) {1}", group.Key, group.Count()))
        Next 

        ' The output is similar to: 
        ' (Key) Method (Member count) 113 
        ' (Key) Constructor (Member count) 8 
        ' (Key) Property (Member count) 2 
        ' (Key) Field (Member count) 1

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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