Enumerable.GroupBy(Of TSource, TKey, TElement, TResult) Method (IEnumerable(Of TSource), Func(Of TSource, TKey), Func(Of TSource, TElement), Func(Of TKey, IEnumerable(Of TElement), TResult), IEqualityComparer(Of TKey))
Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function.
Assembly: System.Core (in System.Core.dll)
<ExtensionAttribute> Public Shared Function GroupBy(Of TSource, TKey, TElement, TResult) ( source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement), resultSelector As Func(Of TKey, IEnumerable(Of TElement), TResult), comparer As IEqualityComparer(Of TKey) ) As IEnumerable(Of TResult)
Parameters
- source
-
Type:
System.Collections.Generic.IEnumerable(Of TSource)
An IEnumerable(Of T) whose elements to group.
- keySelector
-
Type:
System.Func(Of TSource, TKey)
A function to extract the key for each element.
- elementSelector
-
Type:
System.Func(Of TSource, TElement)
A function to map each source element to an element in an IGrouping(Of TKey, TElement).
- resultSelector
-
Type:
System.Func(Of TKey, IEnumerable(Of TElement), TResult)
A function to create a result value from each group.
- comparer
-
Type:
System.Collections.Generic.IEqualityComparer(Of TKey)
An IEqualityComparer(Of T) to compare keys with.
Return Value
Type: System.Collections.Generic.IEnumerable(Of TResult)A collection of elements of type TResult where each element represents a projection over a group and its key.
Type Parameters
- TSource
The type of the elements of source.
- TKey
The type of the key returned by keySelector.
- TElement
The type of the elements in each IGrouping(Of TKey, TElement).
- TResult
The type of the result value returned by resultSelector.
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1