IGrouping<TKey,TElement> Interface

Definition

Represents a collection of objects that have a common key.

generic <typename TKey, typename TElement>
public interface class IGrouping : System::Collections::Generic::IEnumerable<TElement>
public interface IGrouping<out TKey,out TElement> : System.Collections.Generic.IEnumerable<out TElement>
type IGrouping<'Key, 'Element> = interface
    interface seq<'Element>
    interface IEnumerable
Public Interface IGrouping(Of Out TKey, Out TElement)
Implements IEnumerable(Of Out TElement)

Type Parameters

TKey

The type of the key of the IGrouping<TKey,TElement>.

This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
TElement

The type of the values in the IGrouping<TKey,TElement>.

This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
Implements

Examples

The following example demonstrates how to work with an IGrouping<TKey,TElement> object.

In this example, GroupBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) is called on the array of MemberInfo objects returned by GetMembers. GroupBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) groups the objects based on the value of their MemberType property. Each unique value for MemberType in the array of MemberInfo objects becomes a key for a new IGrouping<TKey,TElement> object, and the MemberInfo objects that have that key form the IGrouping<TKey,TElement> object's sequence of values.

Finally, the First method is called on the sequence of IGrouping<TKey,TElement> objects to obtain just the first IGrouping<TKey,TElement> object.

The example then outputs the key of the IGrouping<TKey,TElement> object and the Name property of each value in the IGrouping<TKey,TElement> object's sequence of values. Notice that to access an IGrouping<TKey,TElement> object's sequence of values, you simply use the IGrouping<TKey,TElement> variable itself.

// Get an IGrouping object.
IGrouping<System.Reflection.MemberTypes, System.Reflection.MemberInfo> group =
    typeof(String).GetMembers().
    GroupBy(member => member.MemberType).
    First();

// Output the key of the IGrouping, then iterate
// through each value in the sequence of values
// of the IGrouping and output its Name property.
Console.WriteLine("\nValues that have the key '{0}':", group.Key);
foreach (System.Reflection.MemberInfo mi in group)
    Console.WriteLine(mi.Name);

// The output is similar to:

// Values that have the key 'Method':
// get_Chars
// get_Length
// IndexOf
// IndexOfAny
// LastIndexOf
// LastIndexOfAny
// Insert
// Replace
// Replace
// Remove
// Join
// Join
// Equals
// Equals
// Equals
// ...

' Get an IGrouping object.
Dim group As IGrouping(Of System.Reflection.MemberTypes, System.Reflection.MemberInfo) = _
    Type.GetType("String").GetMembers(). _
    GroupBy(Function(ByVal member) member.MemberType). _
    First()

' Output the key of the IGrouping, then iterate
' through each value in the sequence of values
' of the IGrouping and output its Name property.
MsgBox(String.Format("\nValues that have the key '{0}':", group.Key))
For Each mi As System.Reflection.MemberInfo In group
    MsgBox(mi.Name)
Next

' The output is similar to:

' Values that have the key 'Method':
' get_Chars
' get_Length
' IndexOf
' IndexOfAny
' LastIndexOf
' LastIndexOfAny
' Insert
' Replace
' Replace
' Remove
' Join
' Join
' Equals
' Equals
' Equals
' ...

Remarks

An IGrouping<TKey,TElement> is an IEnumerable<T> that additionally has a key. The key represents the attribute that is common to each value in the IGrouping<TKey,TElement>.

The values of an IGrouping<TKey,TElement> are accessed much as the elements of an IEnumerable<T> are accessed. For example, you can access the values by using a foreach in Visual C# or For Each in Visual Basic loop to iterate through the IGrouping<TKey,TElement> object. The Example section contains a code example that shows you how to access both the key and the values of an IGrouping<TKey,TElement> object.

The IGrouping<TKey,TElement> type is used by the GroupBy standard query operator methods, which return a sequence of elements of type IGrouping<TKey,TElement>.

Properties

Key

Gets the key of the IGrouping<TKey,TElement>.

Methods

GetEnumerator()

Returns an enumerator that iterates through a collection.

(Inherited from IEnumerable)

Extension Methods

CopyToDataTable<T>(IEnumerable<T>)

Returns a DataTable that contains copies of the DataRow objects, given an input IEnumerable<T> object where the generic parameter T is DataRow.

CopyToDataTable<T>(IEnumerable<T>, DataTable, LoadOption)

Copies DataRow objects to the specified DataTable, given an input IEnumerable<T> object where the generic parameter T is DataRow.

CopyToDataTable<T>(IEnumerable<T>, DataTable, LoadOption, FillErrorEventHandler)

Copies DataRow objects to the specified DataTable, given an input IEnumerable<T> object where the generic parameter T is DataRow.

Cast<TResult>(IEnumerable)

Casts the elements of an IEnumerable to the specified type.

OfType<TResult>(IEnumerable)

Filters the elements of an IEnumerable based on a specified type.

AsParallel(IEnumerable)

Enables parallelization of a query.

AsQueryable(IEnumerable)

Converts an IEnumerable to an IQueryable.

Ancestors<T>(IEnumerable<T>)

Returns a collection of elements that contains the ancestors of every node in the source collection.

Ancestors<T>(IEnumerable<T>, XName)

Returns a filtered collection of elements that contains the ancestors of every node in the source collection. Only elements that have a matching XName are included in the collection.

DescendantNodes<T>(IEnumerable<T>)

Returns a collection of the descendant nodes of every document and element in the source collection.

Descendants<T>(IEnumerable<T>)

Returns a collection of elements that contains the descendant elements of every element and document in the source collection.

Descendants<T>(IEnumerable<T>, XName)

Returns a filtered collection of elements that contains the descendant elements of every element and document in the source collection. Only elements that have a matching XName are included in the collection.

Elements<T>(IEnumerable<T>)

Returns a collection of the child elements of every element and document in the source collection.

Elements<T>(IEnumerable<T>, XName)

Returns a filtered collection of the child elements of every element and document in the source collection. Only elements that have a matching XName are included in the collection.

InDocumentOrder<T>(IEnumerable<T>)

Returns a collection of nodes that contains all nodes in the source collection, sorted in document order.

Nodes<T>(IEnumerable<T>)

Returns a collection of the child nodes of every document and element in the source collection.

Remove<T>(IEnumerable<T>)

Removes every node in the source collection from its parent node.

Applies to