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11/18/2011

IGrouping<TKey, TElement> Interface

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Represents a collection of objects that have a common key.

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

Syntax

'Declaration
Public Interface IGrouping(Of Out TKey, Out TElement) _
    Inherits IEnumerable(Of TElement), IEnumerable

public interface IGrouping<out TKey, out TElement> : IEnumerable<TElement>, 
    IEnumerable

Type Parameters

outTKey
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 2678dc63-c7f9-4590-9ddc-0a4df684d42e.

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

The IGrouping<TKey, TElement> type exposes the following members.

Properties

	Name	Description
	Key	Gets the key of the IGrouping<TKey, TElement>.

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Methods

	Name	Description
	GetEnumerator()	Returns an enumerator that iterates through a collection. (Inherited from IEnumerable.)
	GetEnumerator()	Returns an enumerator that iterates through the collection. (Inherited from IEnumerable<T>.)

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Extension Methods

	Name	Description
	Aggregate<TElement>(Func<TElement, TElement, TElement>)	Overloaded. Applies an accumulator function over a sequence. (Defined by Enumerable.)
	Aggregate<TElement, TAccumulate>(TAccumulate, Func<TAccumulate, TElement, TAccumulate>)	Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value. (Defined by Enumerable.)
	Aggregate<TElement, TAccumulate, TResult>(TAccumulate, Func<TAccumulate, TElement, TAccumulate>, Func<TAccumulate, TResult>)	Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value, and the specified function is used to select the result value. (Defined by Enumerable.)
	All<TElement>	Determines whether all elements of a sequence satisfy a condition. (Defined by Enumerable.)
	Any<TElement>()	Overloaded. Determines whether a sequence contains any elements. (Defined by Enumerable.)
	Any<TElement>(Func<TElement, Boolean>)	Overloaded. Determines whether any element of a sequence satisfies a condition. (Defined by Enumerable.)
	AsEnumerable<TElement>	Returns the input typed as IEnumerable<T>. (Defined by Enumerable.)
	AsQueryable()	Overloaded. Converts an IEnumerable to an IQueryable. (Defined by Queryable.)
	AsQueryable<TElement>()	Overloaded. Converts a generic IEnumerable<T> to a generic IQueryable<T>. (Defined by Queryable.)
	Average<TElement>(Func<TElement, Decimal>)	Overloaded. Computes the average of a sequence of Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<TElement>(Func<TElement, Nullable<Decimal>>)	Overloaded. Computes the average of a sequence of nullable Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<TElement>(Func<TElement, Double>)	Overloaded. Computes the average of a sequence of Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<TElement>(Func<TElement, Nullable<Double>>)	Overloaded. Computes the average of a sequence of nullable Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<TElement>(Func<TElement, Int32>)	Overloaded. Computes the average of a sequence of Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<TElement>(Func<TElement, Nullable<Int32>>)	Overloaded. Computes the average of a sequence of nullable Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<TElement>(Func<TElement, Int64>)	Overloaded. Computes the average of a sequence of Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<TElement>(Func<TElement, Nullable<Int64>>)	Overloaded. Computes the average of a sequence of nullable Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<TElement>(Func<TElement, Single>)	Overloaded. Computes the average of a sequence of Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Average<TElement>(Func<TElement, Nullable<Single>>)	Overloaded. Computes the average of a sequence of nullable Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Cast<TResult>	Converts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
	Concat<TElement>	Concatenates two sequences. (Defined by Enumerable.)
	Contains<TElement>(TElement)	Overloaded. Determines whether a sequence contains a specified element by using the default equality comparer. (Defined by Enumerable.)
	Contains<TElement>(TElement, IEqualityComparer<TElement>)	Overloaded. Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
	Count<TElement>()	Overloaded. Returns the number of elements in a sequence. (Defined by Enumerable.)
	Count<TElement>(Func<TElement, Boolean>)	Overloaded. Returns a number that represents how many elements in the specified sequence satisfy a condition. (Defined by Enumerable.)
	DefaultIfEmpty<TElement>()	Overloaded. Returns the elements of the specified sequence or the type parameter's default value in a singleton collection if the sequence is empty. (Defined by Enumerable.)
	DefaultIfEmpty<TElement>(TElement)	Overloaded. Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty. (Defined by Enumerable.)
	Distinct<TElement>()	Overloaded. Returns distinct elements from a sequence by using the default equality comparer to compare values. (Defined by Enumerable.)
	Distinct<TElement>(IEqualityComparer<TElement>)	Overloaded. Returns distinct elements from a sequence by using a specified IEqualityComparer<T> to compare values. (Defined by Enumerable.)
	ElementAt<TElement>	Returns the element at a specified index in a sequence. (Defined by Enumerable.)
	ElementAtOrDefault<TElement>	Returns the element at a specified index in a sequence or a default value if the index is out of range. (Defined by Enumerable.)
	Except<TElement>(IEnumerable<TElement>)	Overloaded. Produces the set difference of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
	Except<TElement>(IEnumerable<TElement>, IEqualityComparer<TElement>)	Overloaded. Produces the set difference of two sequences by using the specified IEqualityComparer<T> to compare values. (Defined by Enumerable.)
	First<TElement>()	Overloaded. Returns the first element of a sequence. (Defined by Enumerable.)
	First<TElement>(Func<TElement, Boolean>)	Overloaded. Returns the first element in a sequence that satisfies a specified condition. (Defined by Enumerable.)
	FirstOrDefault<TElement>()	Overloaded. Returns the first element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
	FirstOrDefault<TElement>(Func<TElement, Boolean>)	Overloaded. Returns the first element of the sequence that satisfies a condition or a default value if no such element is found. (Defined by Enumerable.)
	GroupBy<TElement, TKey>(Func<TElement, TKey>)	Overloaded. Groups the elements of a sequence according to a specified key selector function. (Defined by Enumerable.)
	GroupBy<TElement, TKey>(Func<TElement, TKey>, IEqualityComparer<TKey>)	Overloaded. Groups the elements of a sequence according to a specified key selector function and compares the keys by using a specified comparer. (Defined by Enumerable.)
	GroupBy<TElement, TKey, TElement>(Func<TElement, TKey>, Func<TElement, TElement>)	Overloaded. Groups the elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function. (Defined by Enumerable.)
	GroupBy<TElement, TKey, TResult>(Func<TElement, TKey>, Func<TKey, IEnumerable<TElement>, TResult>)	Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. (Defined by Enumerable.)
	GroupBy<TElement, TKey, TElement>(Func<TElement, TKey>, Func<TElement, TElement>, IEqualityComparer<TKey>)	Overloaded. Groups the elements of a sequence according to a key selector function. The keys are compared by using a comparer and each group's elements are projected by using a specified function. (Defined by Enumerable.)
	GroupBy<TElement, TKey, TResult>(Func<TElement, TKey>, Func<TKey, IEnumerable<TElement>, TResult>, IEqualityComparer<TKey>)	Overloaded. 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. (Defined by Enumerable.)
	GroupBy<TElement, TKey, TElement, TResult>(Func<TElement, TKey>, Func<TElement, TElement>, Func<TKey, IEnumerable<TElement>, TResult>)	Overloaded. 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 elements of each group are projected by using a specified function. (Defined by Enumerable.)
	GroupBy<TElement, TKey, TElement, TResult>(Func<TElement, TKey>, Func<TElement, TElement>, Func<TKey, IEnumerable<TElement>, TResult>, IEqualityComparer<TKey>)	Overloaded. 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. (Defined by Enumerable.)
	GroupJoin<TElement, TInner, TKey, TResult>(IEnumerable<TInner>, Func<TElement, TKey>, Func<TInner, TKey>, Func<TElement, IEnumerable<TInner>, TResult>)	Overloaded. Correlates the elements of two sequences based on equality of keys and groups the results. The default equality comparer is used to compare keys. (Defined by Enumerable.)
	GroupJoin<TElement, TInner, TKey, TResult>(IEnumerable<TInner>, Func<TElement, TKey>, Func<TInner, TKey>, Func<TElement, IEnumerable<TInner>, TResult>, IEqualityComparer<TKey>)	Overloaded. Correlates the elements of two sequences based on key equality and groups the results. A specified IEqualityComparer<T> is used to compare keys. (Defined by Enumerable.)
	Intersect<TElement>(IEnumerable<TElement>)	Overloaded. Produces the set intersection of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
	Intersect<TElement>(IEnumerable<TElement>, IEqualityComparer<TElement>)	Overloaded. Produces the set intersection of two sequences by using the specified IEqualityComparer<T> to compare values. (Defined by Enumerable.)
	Join<TElement, TInner, TKey, TResult>(IEnumerable<TInner>, Func<TElement, TKey>, Func<TInner, TKey>, Func<TElement, TInner, TResult>)	Overloaded. Correlates the elements of two sequences based on matching keys. The default equality comparer is used to compare keys. (Defined by Enumerable.)
	Join<TElement, TInner, TKey, TResult>(IEnumerable<TInner>, Func<TElement, TKey>, Func<TInner, TKey>, Func<TElement, TInner, TResult>, IEqualityComparer<TKey>)	Overloaded. Correlates the elements of two sequences based on matching keys. A specified IEqualityComparer<T> is used to compare keys. (Defined by Enumerable.)
	Last<TElement>()	Overloaded. Returns the last element of a sequence. (Defined by Enumerable.)
	Last<TElement>(Func<TElement, Boolean>)	Overloaded. Returns the last element of a sequence that satisfies a specified condition. (Defined by Enumerable.)
	LastOrDefault<TElement>()	Overloaded. Returns the last element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
	LastOrDefault<TElement>(Func<TElement, Boolean>)	Overloaded. Returns the last element of a sequence that satisfies a condition or a default value if no such element is found. (Defined by Enumerable.)
	LongCount<TElement>()	Overloaded. Returns an Int64 that represents the total number of elements in a sequence. (Defined by Enumerable.)
	LongCount<TElement>(Func<TElement, Boolean>)	Overloaded. Returns an Int64 that represents how many elements in a sequence satisfy a condition. (Defined by Enumerable.)
	Max<TElement>()	Overloaded. Returns the maximum value in a generic sequence. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Decimal>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Decimal value. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Nullable<Decimal>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Decimal value. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Double>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Double value. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Nullable<Double>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Double value. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Int32>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int32 value. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Nullable<Int32>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int32 value. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Int64>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int64 value. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Nullable<Int64>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int64 value. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Single>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Single value. (Defined by Enumerable.)
	Max<TElement>(Func<TElement, Nullable<Single>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Single value. (Defined by Enumerable.)
	Max<TElement, TResult>(Func<TElement, TResult>)	Overloaded. Invokes a transform function on each element of a generic sequence and returns the maximum resulting value. (Defined by Enumerable.)
	Min<TElement>()	Overloaded. Returns the minimum value in a generic sequence. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Decimal>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Decimal value. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Nullable<Decimal>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Decimal value. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Double>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Double value. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Nullable<Double>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Double value. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Int32>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int32 value. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Nullable<Int32>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int32 value. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Int64>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int64 value. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Nullable<Int64>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int64 value. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Single>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Single value. (Defined by Enumerable.)
	Min<TElement>(Func<TElement, Nullable<Single>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Single value. (Defined by Enumerable.)
	Min<TElement, TResult>(Func<TElement, TResult>)	Overloaded. Invokes a transform function on each element of a generic sequence and returns the minimum resulting value. (Defined by Enumerable.)
	OfType<TResult>	Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)
	OrderBy<TElement, TKey>(Func<TElement, TKey>)	Overloaded. Sorts the elements of a sequence in ascending order according to a key. (Defined by Enumerable.)
	OrderBy<TElement, TKey>(Func<TElement, TKey>, IComparer<TKey>)	Overloaded. Sorts the elements of a sequence in ascending order by using a specified comparer. (Defined by Enumerable.)
	OrderByDescending<TElement, TKey>(Func<TElement, TKey>)	Overloaded. Sorts the elements of a sequence in descending order according to a key. (Defined by Enumerable.)
	OrderByDescending<TElement, TKey>(Func<TElement, TKey>, IComparer<TKey>)	Overloaded. Sorts the elements of a sequence in descending order by using a specified comparer. (Defined by Enumerable.)
	Reverse<TElement>	Inverts the order of the elements in a sequence. (Defined by Enumerable.)
	Select<TElement, TResult>(Func<TElement, TResult>)	Overloaded. Projects each element of a sequence into a new form. (Defined by Enumerable.)
	Select<TElement, TResult>(Func<TElement, Int32, TResult>)	Overloaded. Projects each element of a sequence into a new form by incorporating the element's index. (Defined by Enumerable.)
	SelectMany<TElement, TResult>(Func<TElement, IEnumerable<TResult>>)	Overloaded. Projects each element of a sequence to an IEnumerable<T> and flattens the resulting sequences into one sequence. (Defined by Enumerable.)
	SelectMany<TElement, TResult>(Func<TElement, Int32, IEnumerable<TResult>>)	Overloaded. Projects each element of a sequence to an IEnumerable<T>, and flattens the resulting sequences into one sequence. The index of each source element is used in the projected form of that element. (Defined by Enumerable.)
	SelectMany<TElement, TCollection, TResult>(Func<TElement, Int32, IEnumerable<TCollection>>, Func<TElement, TCollection, TResult>)	Overloaded. Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. The index of each source element is used in the intermediate projected form of that element. (Defined by Enumerable.)
	SelectMany<TElement, TCollection, TResult>(Func<TElement, IEnumerable<TCollection>>, Func<TElement, TCollection, TResult>)	Overloaded. Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. (Defined by Enumerable.)
	SequenceEqual<TElement>(IEnumerable<TElement>)	Overloaded. Determines whether two sequences are equal by comparing the elements by using the default equality comparer for their type. (Defined by Enumerable.)
	SequenceEqual<TElement>(IEnumerable<TElement>, IEqualityComparer<TElement>)	Overloaded. Determines whether two sequences are equal by comparing their elements by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
	Single<TElement>()	Overloaded. Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence. (Defined by Enumerable.)
	Single<TElement>(Func<TElement, Boolean>)	Overloaded. Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists. (Defined by Enumerable.)
	SingleOrDefault<TElement>()	Overloaded. Returns the only element of a sequence, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence. (Defined by Enumerable.)
	SingleOrDefault<TElement>(Func<TElement, Boolean>)	Overloaded. Returns the only element of a sequence that satisfies a specified condition or a default value if no such element exists; this method throws an exception if more than one element satisfies the condition. (Defined by Enumerable.)
	Skip<TElement>	Bypasses a specified number of elements in a sequence and then returns the remaining elements. (Defined by Enumerable.)
	SkipWhile<TElement>(Func<TElement, Boolean>)	Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. (Defined by Enumerable.)
	SkipWhile<TElement>(Func<TElement, Int32, Boolean>)	Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. The element's index is used in the logic of the predicate function. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Decimal>)	Overloaded. Computes the sum of the sequence of Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Nullable<Decimal>>)	Overloaded. Computes the sum of the sequence of nullable Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Double>)	Overloaded. Computes the sum of the sequence of Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Nullable<Double>>)	Overloaded. Computes the sum of the sequence of nullable Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Int32>)	Overloaded. Computes the sum of the sequence of Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Nullable<Int32>>)	Overloaded. Computes the sum of the sequence of nullable Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Int64>)	Overloaded. Computes the sum of the sequence of Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Nullable<Int64>>)	Overloaded. Computes the sum of the sequence of nullable Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Single>)	Overloaded. Computes the sum of the sequence of Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Sum<TElement>(Func<TElement, Nullable<Single>>)	Overloaded. Computes the sum of the sequence of nullable Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
	Take<TElement>	Returns a specified number of contiguous elements from the start of a sequence. (Defined by Enumerable.)
	TakeWhile<TElement>(Func<TElement, Boolean>)	Overloaded. Returns elements from a sequence as long as a specified condition is true. (Defined by Enumerable.)
	TakeWhile<TElement>(Func<TElement, Int32, Boolean>)	Overloaded. Returns elements from a sequence as long as a specified condition is true. The element's index is used in the logic of the predicate function. (Defined by Enumerable.)
	ToArray<TElement>	Creates an array from a IEnumerable<T>. (Defined by Enumerable.)
	ToDictionary<TElement, TKey>(Func<TElement, TKey>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function. (Defined by Enumerable.)
	ToDictionary<TElement, TKey>(Func<TElement, TKey>, IEqualityComparer<TKey>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function and key comparer. (Defined by Enumerable.)
	ToDictionary<TElement, TKey, TElement>(Func<TElement, TKey>, Func<TElement, TElement>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to specified key selector and element selector functions. (Defined by Enumerable.)
	ToDictionary<TElement, TKey, TElement>(Func<TElement, TKey>, Func<TElement, TElement>, IEqualityComparer<TKey>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function, a comparer, and an element selector function. (Defined by Enumerable.)
	ToList<TElement>	Creates a List<T> from an IEnumerable<T>. (Defined by Enumerable.)
	ToLookup<TElement, TKey>(Func<TElement, TKey>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function. (Defined by Enumerable.)
	ToLookup<TElement, TKey>(Func<TElement, TKey>, IEqualityComparer<TKey>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function and key comparer. (Defined by Enumerable.)
	ToLookup<TElement, TKey, TElement>(Func<TElement, TKey>, Func<TElement, TElement>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to specified key selector and element selector functions. (Defined by Enumerable.)
	ToLookup<TElement, TKey, TElement>(Func<TElement, TKey>, Func<TElement, TElement>, IEqualityComparer<TKey>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function, a comparer and an element selector function. (Defined by Enumerable.)
	Union<TElement>(IEnumerable<TElement>)	Overloaded. Produces the set union of two sequences by using the default equality comparer. (Defined by Enumerable.)
	Union<TElement>(IEnumerable<TElement>, IEqualityComparer<TElement>)	Overloaded. Produces the set union of two sequences by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
	Where<TElement>(Func<TElement, Boolean>)	Overloaded. Filters a sequence of values based on a predicate. (Defined by Enumerable.)
	Where<TElement>(Func<TElement, Int32, Boolean>)	Overloaded. Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function. (Defined by Enumerable.)
	Zip<TElement, TSecond, TResult>	Merges two sequences by using the specified predicate function. (Defined by Enumerable.)

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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>.

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.
      Dim group As IGrouping(Of System.Reflection.MemberTypes, System.Reflection.MemberInfo) = _
          Type.GetType("System.String").GetMembers(). _
          GroupBy(Function(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.
      outputBlock.Text &= (String.Format("Values that have the key '{0}':", group.Key) & vbCrLf)
      For Each mi As System.Reflection.MemberInfo In group
         outputBlock.Text &= mi.Name & vbCrLf
      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
      ' ...

      // 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.
      outputBlock.Text += String.Format("\nValues that have the key '{0}':", group.Key) + "\n";
      foreach (System.Reflection.MemberInfo mi in group)
         outputBlock.Text += mi.Name + "\n";

      // 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
      // ...

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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