Enumerable.GroupBy<TSource, TKey, TElement, TResult> Method (IEnumerable<TSource>, Func<TSource, TKey>, Func<TSource, TElement>, Func<TKey, IEnumerable<TElement>, 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. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
public static IEnumerable<TResult> GroupBy<TSource, TKey, TElement, TResult>( this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TSource, TElement> elementSelector, Func<TKey, IEnumerable<TElement>, TResult> resultSelector, IEqualityComparer<TKey> comparer )
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<TKey, TElement>.
- 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.
- elementSelector
- Type: System.Func<TSource, TElement>
A function to map each source element to an element in an IGrouping<TKey, TElement>.
- resultSelector
- Type: System.Func<TKey, IEnumerable<TElement>, 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 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
