Enumerable.GroupBy<TSource, TKey, TResult> Method (IEnumerable<TSource>, Func<TSource, TKey>, Func<TKey, IEnumerable<TSource>, TResult>, IEqualityComparer<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. The keys are compared by using a specified comparer.
Assembly: System.Core (in System.Core.dll)
public static IEnumerable<TResult> GroupBy<TSource, TKey, TResult>( this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, IEnumerable<TSource>, TResult> resultSelector, IEqualityComparer<TKey> comparer )
Type Parameters
- TSource
The type of the elements of source.
- TKey
The type of the key returned by keySelector.
- TResult
The type of the result value returned by resultSelector.
Parameters
- source
- Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> whose elements to group.
- keySelector
- Type: System.Func<TSource, TKey>
A function to extract the key for each element.
- resultSelector
- Type: System.Func<TKey, IEnumerable<TSource>, TResult>
A function to create a result value from each group.
- comparer
- Type: System.Collections.Generic.IEqualityComparer<TKey>
An IEqualityComparer<T> to compare keys with.
Return Value
Type: System.Collections.Generic.IEnumerable<TResult>A collection of elements of type TResult where each element represents a projection over a group and its key.
Usage Note
In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.