IEnumerable Interface

IEnumerable<T> Interface

.NET Framework 4.5

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Exposes the enumerator, which supports a simple iteration over a collection of a specified type.

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

Syntax

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C#

C++

F#

VB

public interface IEnumerable<out T> : IEnumerable

Type Parameters

outT

The type of objects to enumerate.

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.

The IEnumerable<T> type exposes the following members.

Methods

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

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Extension Methods

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	Name	Description
	Aggregate<TSource>(Func<TSource, TSource, TSource>)	Overloaded. Applies an accumulator function over a sequence. (Defined byEnumerable.)
	Aggregate<TSource, TAccumulate>(TAccumulate, Func<TAccumulate, TSource, TAccumulate>)	Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value. (Defined by Enumerable.)
	Aggregate<TSource, TAccumulate, TResult>(TAccumulate, Func<TAccumulate, TSource, 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<TSource>	Determines whether all elements of a sequence satisfy a condition. (Defined by Enumerable.)
	Ancestors<T>()	Overloaded. Returns a collection of elements that contains the ancestors of every node in the source collection. (Defined by Extensions.)
	Ancestors<T>(XName)	Overloaded. 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. (Defined by Extensions.)
	Any<TSource>()	Overloaded. Determines whether a sequence contains any elements. (Defined by Enumerable.)
	Any<TSource>(Func<TSource, Boolean>)	Overloaded. Determines whether any element of a sequence satisfies a condition. (Defined by Enumerable.)
	AsEnumerable<TSource>	Returns the input typed as IEnumerable<T>. (Defined by Enumerable.)
	AsParallel()	Overloaded. Enables parallelization of a query. (Defined byParallelEnumerable.)
	AsParallel<TSource>()	Overloaded. Enables parallelization of a query. (Defined byParallelEnumerable.)
	AsQueryable()	Overloaded. Converts an IEnumerable to an IQueryable. (Defined byQueryable.)
	AsQueryable<TElement>()	Overloaded. Converts a generic IEnumerable<T> to a generic IQueryable<T>.(Defined by Queryable.)
	Average<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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>	Casts the elements of an IEnumerable to the specified type. (Defined byEnumerable.)
	Concat<TSource>	Concatenates two sequences. (Defined by Enumerable.)
	Contains<TSource>(TSource)	Overloaded. Determines whether a sequence contains a specified element by using the default equality comparer. (Defined by Enumerable.)
	Contains<TSource>(TSource, IEqualityComparer<TSource>)	Overloaded. Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
	CopyToDataTable<T>()	Overloaded. Returns a DataTable that contains copies of the DataRowobjects, given an input IEnumerable<T> object where the generic parameterT is DataRow. (Defined by DataTableExtensions.)
	CopyToDataTable<T>(DataTable, LoadOption)	Overloaded. Copies DataRow objects to the specified DataTable, given an input IEnumerable<T> object where the generic parameter T is DataRow.(Defined by DataTableExtensions.)
	CopyToDataTable<T>(DataTable, LoadOption, FillErrorEventHandler)	Overloaded. Copies DataRow objects to the specified DataTable, given an input IEnumerable<T> object where the generic parameter T is DataRow.(Defined by DataTableExtensions.)
	Count<TSource>()	Overloaded. Returns the number of elements in a sequence. (Defined byEnumerable.)
	Count<TSource>(Func<TSource, Boolean>)	Overloaded. Returns a number that represents how many elements in the specified sequence satisfy a condition. (Defined by Enumerable.)
	DefaultIfEmpty<TSource>()	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<TSource>(TSource)	Overloaded. Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty. (Defined byEnumerable.)
	DescendantNodes<T>	Returns a collection of the descendant nodes of every document and element in the source collection. (Defined by Extensions.)
	Descendants<T>()	Overloaded. Returns a collection of elements that contains the descendant elements of every element and document in the source collection. (Defined by Extensions.)
	Descendants<T>(XName)	Overloaded. 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. (Defined by Extensions.)
	Distinct<TSource>()	Overloaded. Returns distinct elements from a sequence by using the default equality comparer to compare values. (Defined by Enumerable.)
	Distinct<TSource>(IEqualityComparer<TSource>)	Overloaded. Returns distinct elements from a sequence by using a specifiedIEqualityComparer<T> to compare values. (Defined by Enumerable.)
	ElementAt<TSource>	Returns the element at a specified index in a sequence. (Defined byEnumerable.)
	ElementAtOrDefault<TSource>	Returns the element at a specified index in a sequence or a default value if the index is out of range. (Defined by Enumerable.)
	Elements<T>()	Overloaded. Returns a collection of the child elements of every element and document in the source collection. (Defined by Extensions.)
	Elements<T>(XName)	Overloaded. 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. (Defined by Extensions.)
	Except<TSource>(IEnumerable<TSource>)	Overloaded. Produces the set difference of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
	Except<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>)	Overloaded. Produces the set difference of two sequences by using the specified IEqualityComparer<T> to compare values. (Defined byEnumerable.)
	First<TSource>()	Overloaded. Returns the first element of a sequence. (Defined byEnumerable.)
	First<TSource>(Func<TSource, Boolean>)	Overloaded. Returns the first element in a sequence that satisfies a specified condition. (Defined by Enumerable.)
	FirstOrDefault<TSource>()	Overloaded. Returns the first element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
	FirstOrDefault<TSource>(Func<TSource, Boolean>)	Overloaded. Returns the first element of the sequence that satisfies a condition or a default value if no such element is found. (Defined byEnumerable.)
	GroupBy<TSource, TKey>(Func<TSource, TKey>)	Overloaded. Groups the elements of a sequence according to a specified key selector function. (Defined by Enumerable.)
	GroupBy<TSource, TKey>(Func<TSource, 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<TSource, TKey, TElement>(Func<TSource, TKey>, Func<TSource, 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<TSource, TKey, TResult>(Func<TSource, TKey>, Func<TKey, IEnumerable<TSource>, 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<TSource, TKey, TElement>(Func<TSource, TKey>, Func<TSource, 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 byEnumerable.)
	GroupBy<TSource, TKey, TResult>(Func<TSource, TKey>, Func<TKey, IEnumerable<TSource>, 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<TSource, TKey, TElement, TResult>(Func<TSource, TKey>, Func<TSource, 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<TSource, TKey, TElement, TResult>(Func<TSource, TKey>, Func<TSource, 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 byEnumerable.)
	GroupJoin<TOuter, TInner, TKey, TResult>(IEnumerable<TInner>, Func<TOuter, TKey>, Func<TInner, TKey>, Func<TOuter, 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<TOuter, TInner, TKey, TResult>(IEnumerable<TInner>, Func<TOuter, TKey>, Func<TInner, TKey>, Func<TOuter, 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.)
	InDocumentOrder<T>	Returns a collection of nodes that contains all nodes in the source collection, sorted in document order. (Defined by Extensions.)
	Intersect<TSource>(IEnumerable<TSource>)	Overloaded. Produces the set intersection of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
	Intersect<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>)	Overloaded. Produces the set intersection of two sequences by using the specified IEqualityComparer<T> to compare values. (Defined byEnumerable.)
	Join<TOuter, TInner, TKey, TResult>(IEnumerable<TInner>, Func<TOuter, TKey>, Func<TInner, TKey>, Func<TOuter, TInner, TResult>)	Overloaded. Correlates the elements of two sequences based on matching keys. The default equality comparer is used to compare keys. (Defined byEnumerable.)
	Join<TOuter, TInner, TKey, TResult>(IEnumerable<TInner>, Func<TOuter, TKey>, Func<TInner, TKey>, Func<TOuter, 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 byEnumerable.)
	Last<TSource>()	Overloaded. Returns the last element of a sequence. (Defined byEnumerable.)
	Last<TSource>(Func<TSource, Boolean>)	Overloaded. Returns the last element of a sequence that satisfies a specified condition. (Defined by Enumerable.)
	LastOrDefault<TSource>()	Overloaded. Returns the last element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
	LastOrDefault<TSource>(Func<TSource, 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<TSource>()	Overloaded. Returns an Int64 that represents the total number of elements in a sequence. (Defined by Enumerable.)
	LongCount<TSource>(Func<TSource, Boolean>)	Overloaded. Returns an Int64 that represents how many elements in a sequence satisfy a condition. (Defined by Enumerable.)
	Max<TSource>()	Overloaded. Returns the maximum value in a generic sequence. (Defined byEnumerable.)
	Max<TSource>(Func<TSource, Decimal>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Decimal value. (Defined by Enumerable.)
	Max<TSource>(Func<TSource, Nullable<Decimal>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Decimal value. (Defined by Enumerable.)
	Max<TSource>(Func<TSource, Double>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Double value. (Defined by Enumerable.)
	Max<TSource>(Func<TSource, Nullable<Double>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Double value. (Defined by Enumerable.)
	Max<TSource>(Func<TSource, Int32>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int32 value. (Defined by Enumerable.)
	Max<TSource>(Func<TSource, Nullable<Int32>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int32 value. (Defined by Enumerable.)
	Max<TSource>(Func<TSource, Int64>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int64 value. (Defined by Enumerable.)
	Max<TSource>(Func<TSource, Nullable<Int64>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int64 value. (Defined by Enumerable.)
	Max<TSource>(Func<TSource, Single>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Single value. (Defined by Enumerable.)
	Max<TSource>(Func<TSource, Nullable<Single>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Single value. (Defined by Enumerable.)
	Max<TSource, TResult>(Func<TSource, TResult>)	Overloaded. Invokes a transform function on each element of a generic sequence and returns the maximum resulting value. (Defined byEnumerable.)
	Min<TSource>()	Overloaded. Returns the minimum value in a generic sequence. (Defined byEnumerable.)
	Min<TSource>(Func<TSource, Decimal>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Decimal value. (Defined by Enumerable.)
	Min<TSource>(Func<TSource, Nullable<Decimal>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Decimal value. (Defined by Enumerable.)
	Min<TSource>(Func<TSource, Double>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Double value. (Defined by Enumerable.)
	Min<TSource>(Func<TSource, Nullable<Double>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Double value. (Defined by Enumerable.)
	Min<TSource>(Func<TSource, Int32>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int32 value. (Defined by Enumerable.)
	Min<TSource>(Func<TSource, Nullable<Int32>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int32 value. (Defined by Enumerable.)
	Min<TSource>(Func<TSource, Int64>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int64 value. (Defined by Enumerable.)
	Min<TSource>(Func<TSource, Nullable<Int64>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int64 value. (Defined by Enumerable.)
	Min<TSource>(Func<TSource, Single>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Single value. (Defined by Enumerable.)
	Min<TSource>(Func<TSource, Nullable<Single>>)	Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Single value. (Defined by Enumerable.)
	Min<TSource, TResult>(Func<TSource, TResult>)	Overloaded. Invokes a transform function on each element of a generic sequence and returns the minimum resulting value. (Defined byEnumerable.)
	Nodes<T>	Returns a collection of the child nodes of every document and element in the source collection. (Defined by Extensions.)
	OfType<TResult>	Filters the elements of an IEnumerable based on a specified type. (Defined byEnumerable.)
	OrderBy<TSource, TKey>(Func<TSource, TKey>)	Overloaded. Sorts the elements of a sequence in ascending order according to a key. (Defined by Enumerable.)
	OrderBy<TSource, TKey>(Func<TSource, TKey>, IComparer<TKey>)	Overloaded. Sorts the elements of a sequence in ascending order by using a specified comparer. (Defined by Enumerable.)
	OrderByDescending<TSource, TKey>(Func<TSource, TKey>)	Overloaded. Sorts the elements of a sequence in descending order according to a key. (Defined by Enumerable.)
	OrderByDescending<TSource, TKey>(Func<TSource, TKey>, IComparer<TKey>)	Overloaded. Sorts the elements of a sequence in descending order by using a specified comparer. (Defined by Enumerable.)
	Remove<T>	Removes every node in the source collection from its parent node. (Defined by Extensions.)
	Reverse<TSource>	Inverts the order of the elements in a sequence. (Defined by Enumerable.)
	Select<TSource, TResult>(Func<TSource, TResult>)	Overloaded. Projects each element of a sequence into a new form. (Defined by Enumerable.)
	Select<TSource, TResult>(Func<TSource, Int32, TResult>)	Overloaded. Projects each element of a sequence into a new form by incorporating the element's index. (Defined by Enumerable.)
	SelectMany<TSource, TResult>(Func<TSource, 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<TSource, TResult>(Func<TSource, 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 byEnumerable.)
	SelectMany<TSource, TCollection, TResult>(Func<TSource, Int32, IEnumerable<TCollection>>, Func<TSource, 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 byEnumerable.)
	SelectMany<TSource, TCollection, TResult>(Func<TSource, IEnumerable<TCollection>>, Func<TSource, 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<TSource>(IEnumerable<TSource>)	Overloaded. Determines whether two sequences are equal by comparing the elements by using the default equality comparer for their type. (Defined byEnumerable.)
	SequenceEqual<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>)	Overloaded. Determines whether two sequences are equal by comparing their elements by using a specified IEqualityComparer<T>. (Defined byEnumerable.)
	Single<TSource>()	Overloaded. Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence. (Defined byEnumerable.)
	Single<TSource>(Func<TSource, 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<TSource>()	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<TSource>(Func<TSource, 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 byEnumerable.)
	Skip<TSource>	Bypasses a specified number of elements in a sequence and then returns the remaining elements. (Defined by Enumerable.)
	SkipWhile<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>(Func<TSource, 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<TSource>	Returns a specified number of contiguous elements from the start of a sequence. (Defined by Enumerable.)
	TakeWhile<TSource>(Func<TSource, Boolean>)	Overloaded. Returns elements from a sequence as long as a specified condition is true. (Defined by Enumerable.)
	TakeWhile<TSource>(Func<TSource, 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<TSource>	Creates an array from a IEnumerable<T>. (Defined by Enumerable.)
	ToDictionary<TSource, TKey>(Func<TSource, TKey>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T>according to a specified key selector function. (Defined by Enumerable.)
	ToDictionary<TSource, TKey>(Func<TSource, TKey>, IEqualityComparer<TKey>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T>according to a specified key selector function and key comparer. (Defined byEnumerable.)
	ToDictionary<TSource, TKey, TElement>(Func<TSource, TKey>, Func<TSource, TElement>)	Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T>according to specified key selector and element selector functions. (Defined by Enumerable.)
	ToDictionary<TSource, TKey, TElement>(Func<TSource, TKey>, Func<TSource, 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<TSource>	Creates a List<T> from an IEnumerable<T>. (Defined by Enumerable.)
	ToLookup<TSource, TKey>(Func<TSource, TKey>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T>according to a specified key selector function. (Defined by Enumerable.)
	ToLookup<TSource, TKey>(Func<TSource, TKey>, IEqualityComparer<TKey>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T>according to a specified key selector function and key comparer. (Defined byEnumerable.)
	ToLookup<TSource, TKey, TElement>(Func<TSource, TKey>, Func<TSource, TElement>)	Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T>according to specified key selector and element selector functions. (Defined by Enumerable.)
	ToLookup<TSource, TKey, TElement>(Func<TSource, TKey>, Func<TSource, 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<TSource>(IEnumerable<TSource>)	Overloaded. Produces the set union of two sequences by using the default equality comparer. (Defined by Enumerable.)
	Union<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>)	Overloaded. Produces the set union of two sequences by using a specifiedIEqualityComparer<T>. (Defined by Enumerable.)
	Where<TSource>(Func<TSource, Boolean>)	Overloaded. Filters a sequence of values based on a predicate. (Defined byEnumerable.)
	Where<TSource>(Func<TSource, 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<TFirst, TSecond, TResult>	Merges two sequences by using the specified predicate function. (Defined byEnumerable.)

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Remarks

---

Many interfaces and classes in the System.Collections.Generic namespace inherit the IEnumerable<T> interface to implement enumerators. For an example, see the ICollection<T> interface.

Notes to Implementers

IEnumerable<T> is included for parity with non-generic collections; implementing IEnumerable<T> allows a generic collection to be passed to a method that expects an IEnumerable object.

LINQ - Grouping Operators

Introduction

This sample shows different uses of Conversion Operators:

• ToArray
• ToList
• ToDictionary
• OfType

Description

ToArray

This sample uses ToArray to immediately evaluate a sequence into an array.

C#

public void Linq54()
{
    double[] doubles = { 1.7, 2.3, 1.9, 4.1, 2.9 };
 
    var sortedDoubles =
        from d in doubles
        orderby d descending
        select d;
    var doublesArray = sortedDoubles.ToArray();
 
    Console.WriteLine("Every other double from highest to lowest:");
    for (int d = 0; d < doublesArray.Length; d += 2)
    {
        Console.WriteLine(doublesArray[d]);
    }
}

Result

Every other double from highest to lowest:
4.1
2.3
1.7

ToList

This sample uses ToList to immediately evaluate a sequence into a List<T>.

C#

public void Linq55()
{
    string[] words = { "cherry", "apple", "blueberry" };
 
    var sortedWords =
        from w in words
        orderby w
        select w;
    var wordList = sortedWords.ToList();
 
    Console.WriteLine("The sorted word list:");
    foreach (var w in wordList)
    {
        Console.WriteLine(w);
    }
}

Result

The sorted word list:
apple
blueberry
cherry

ToDictionary

This sample uses ToDictionary to immediately evaluate a sequence and a related key expression into a dictionary.

C#

public void Linq56()
{
    var scoreRecords = new[] { new {Name = "Alice", Score = 50},
                                new {Name = "Bob"  , Score = 40},
                                new {Name = "Cathy", Score = 45}
                            };
 
    var scoreRecordsDict = scoreRecords.ToDictionary(sr => sr.Name);
 
    Console.WriteLine("Bob's score: {0}", scoreRecordsDict["Bob"]);
}

Result

Bob's score: { Name = Bob, Score = 40 }

OfType

This sample uses OfType to return only the elements of the array that are of type double.

C#

public void Linq57()
{
    object[] numbers = { null, 1.0, "two", 3, "four", 5, "six", 7.0 };
 
    var doubles = numbers.OfType<double>();
 
    Console.WriteLine("Numbers stored as doubles:");
    foreach (var d in doubles)
    {
        Console.WriteLine(d);
    }
}

Result

Numbers stored as doubles:
1
7

LINQ - Aggregate Operators

Introduction

This sample shows different uses of Aggregate Operators:

• Count - Simple
• Count - Conditional
• Count - Nested
• Count - Grouped
• Sum - Simple
• Sum - Projection
• Sum - Grouped
• Min - Simple
• Min - Projection
• Min - Grouped
• Min - Elements
• Max - Simple
• Max - Projection
• Max - Grouped
• Max - Elements
• Average - Simple
• Average - Projection
• Average - Grouped
• Aggregate - Simple
• Aggregate - Seed

Description

Count - Simple  

(back to top)

This sample uses Count to get the number of unique factors of 300.

C#

public void Linq73()
{
    int[] factorsOf300 = { 2, 2, 3, 5, 5 };
 
    int uniqueFactors = factorsOf300.Distinct().Count();
 
    Console.WriteLine("There are {0} unique factors of 300.", uniqueFactors);
}

 Result

There are 3 unique factors of 300.

Count - Conditional

This sample uses Count to get the number of odd ints in the array.

C#

public void Linq74()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
 
    int oddNumbers = numbers.Count(n => n % 2 == 1);
 
    Console.WriteLine("There are {0} odd numbers in the list.", oddNumbers);
}

Result

There are 5 odd numbers in the list.

Count - Nested

This sample uses Count to return a list of customers and how many orders each has.

C#

public void Linq76()
{
    List<Customer> customers = GetCustomerList();
 
    var orderCounts =
        from c in customers
        select new { c.CustomerID, OrderCount = c.Orders.Count() };
 
    ObjectDumper.Write(orderCounts);
}

Result

CustomerID=ALFKI CustomerID=ANATR CustomerID=ANTON CustomerID=AROUT CustomerID=BERGS CustomerID=BLAUS CustomerID=BLONP CustomerID=BOLID CustomerID=BONAP CustomerID=BOTTM CustomerID=BSBEV CustomerID=CACTU CustomerID=CENTC CustomerID=CHOPS CustomerID=COMMI CustomerID=CONSH CustomerID=DRACD CustomerID=DUMON CustomerID=EASTC CustomerID=ERNSH CustomerID=FAMIA CustomerID=FISSA CustomerID=FOLIG CustomerID=FOLKO CustomerID=FRANK CustomerID=FRANR CustomerID=FRANS CustomerID=FURIB CustomerID=GALED CustomerID=GODOS CustomerID=GOURL CustomerID=GREAL CustomerID=GROSR CustomerID=HANAR CustomerID=HILAA CustomerID=HUNGC CustomerID=HUNGO CustomerID=ISLAT CustomerID=KOENE CustomerID=LACOR CustomerID=LAMAI CustomerID=LAUGB CustomerID=LAZYK CustomerID=LEHMS CustomerID=LETSS CustomerID=LILAS CustomerID=LINOD CustomerID=LONEP CustomerID=MAGAA CustomerID=MAISD CustomerID=MEREP CustomerID=MORGK CustomerID=NORTS CustomerID=OCEAN CustomerID=OLDWO CustomerID=OTTIK CustomerID=PARIS CustomerID=PERIC CustomerID=PICCO CustomerID=PRINI CustomerID=QUEDE CustomerID=QUEEN CustomerID=QUICK CustomerID=RANCH CustomerID=RATTC CustomerID=REGGC CustomerID=RICAR CustomerID=RICSU CustomerID=ROMEY CustomerID=SANTG CustomerID=SAVEA CustomerID=SEVES CustomerID=SIMOB CustomerID=SPECD CustomerID=SPLIR CustomerID=SUPRD CustomerID=THEBI CustomerID=THECR CustomerID=TOMSP CustomerID=TORTU CustomerID=TRADH CustomerID=TRAIH CustomerID=VAFFE CustomerID=VICTE CustomerID=VINET CustomerID=WANDK CustomerID=WARTH CustomerID=WELLI CustomerID=WHITC CustomerID=WILMK CustomerID=WOLZA

OrderCount=6 OrderCount=4 OrderCount=7 OrderCount=13 OrderCount=18 OrderCount=7 OrderCount=11 OrderCount=3 OrderCount=17 OrderCount=14 OrderCount=10 OrderCount=6 OrderCount=1 OrderCount=8 OrderCount=5 OrderCount=3 OrderCount=6 OrderCount=4 OrderCount=8 OrderCount=30 OrderCount=7 OrderCount=0 OrderCount=5 OrderCount=19 OrderCount=15 OrderCount=3 OrderCount=6 OrderCount=8 OrderCount=5 OrderCount=10 OrderCount=9 OrderCount=11 OrderCount=2 OrderCount=14 OrderCount=18 OrderCount=5 OrderCount=19 OrderCount=10 OrderCount=14 OrderCount=4 OrderCount=14 OrderCount=3 OrderCount=2 OrderCount=15 OrderCount=4 OrderCount=14 OrderCount=12 OrderCount=8 OrderCount=10 OrderCount=7 OrderCount=13 OrderCount=5 OrderCount=3 OrderCount=5 OrderCount=10 OrderCount=9 OrderCount=0 OrderCount=6 OrderCount=10 OrderCount=6 OrderCount=9 OrderCount=13 OrderCount=28 OrderCount=5 OrderCount=18 OrderCount=12 OrderCount=11 OrderCount=10 OrderCount=5 OrderCount=6 OrderCount=31 OrderCount=9 OrderCount=7 OrderCount=4 OrderCount=9 OrderCount=12 OrderCount=4 OrderCount=3 OrderCount=5 OrderCount=10 OrderCount=7 OrderCount=3 OrderCount=11 OrderCount=10 OrderCount=4 OrderCount=10 OrderCount=15 OrderCount=9 OrderCount=14 OrderCount=8 OrderCount=7

Count - Grouped

This sample uses Count to return a list of categories and how many products each has.

C#

public void Linq77()
{
    List<Product> products = GetProductList();
 
    var categoryCounts =
        from p in products
        group p by p.Category into g
        select new { Category = g.Key, ProductCount = g.Count() };
 
    ObjectDumper.Write(categoryCounts
}

Result

Category=Beverages Category=Condiments Category=Produce Category=Meat/Poultry Category=Seafood Category=Dairy Products Category=Confections Category=Grains/Cereals

ProductCount=12 ProductCount=12 ProductCount=5 ProductCount=6 ProductCount=12 ProductCount=10 ProductCount=13 ProductCount=7

Sum - Simple

This sample uses Sum to get the total of the numbers in an array.

C#

public void Linq78()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
 
    double numSum = numbers.Sum();
 
    Console.WriteLine("The sum of the numbers is {0}.", numSum);
}

 Result

The sum of the numbers is 45.

Sum - Projection

This sample uses Sum to get the total number of characters of all words in the array.

C#

public void Linq79()
{
    string[] words = { "cherry", "apple", "blueberry" };
 
    double totalChars = words.Sum(w => w.Length);
 
    Console.WriteLine("There are a total of {0} characters in these words.", totalChars);
}

Result

There are a total of 20 characters in these words.

Sum - Grouped

This sample uses Sum to get the total units in stock for each product category.

C#

public void Linq80()
{
    List<Product> products = GetProductList();
 
    var categories =
        from p in products
        group p by p.Category into g
        select new { Category = g.Key, TotalUnitsInStock = g.Sum(p => p.UnitsInStock) };
 
    ObjectDumper.Write(categories);
}

Result

Category=Beverages Category=Condiments Category=Produce Category=Meat/Poultry Category=Seafood Category=Dairy Products Category=Confections Category=Grains/Cereals

TotalUnitsInStock=559 TotalUnitsInStock=507 TotalUnitsInStock=100 TotalUnitsInStock=165 TotalUnitsInStock=701 TotalUnitsInStock=393 TotalUnitsInStock=386 TotalUnitsInStock=308

Min - Simple

This sample uses Min to get the lowest number in an array.

C#

public void Linq81()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
 
    int minNum = numbers.Min();
 
    Console.WriteLine("The minimum number is {0}.", minNum);
}

Result

The minimum number is 0.

Min - Projection

This sample uses Min to get the length of the shortest word in an array.

C#

public void Linq82()
{
    string[] words = { "cherry", "apple", "blueberry" };
 
    int shortestWord = words.Min(w => w.Length);
 
    Console.WriteLine("The shortest word is {0} characters long.", shortestWord);
}

Result

The shortest word is 5 characters long.

Min - Grouped

This sample uses Min to get the cheapest price among each category's products.

C#

public void Linq83()
{
    List<Product> products = GetProductList();
 
    var categories =
        from p in products
        group p by p.Category into g
        select new { Category = g.Key, CheapestPrice = g.Min(p => p.UnitPrice) };
 
    ObjectDumper.Write(categories);
}

Result

Category=Beverages Category=Condiments Category=Produce Category=Meat/Poultry Category=Seafood Category=Dairy Products Category=Confections Category=Grains/Cereals

CheapestPrice=4.5000 CheapestPrice=10.0000 CheapestPrice=10.0000 CheapestPrice=7.4500 CheapestPrice=6.0000 CheapestPrice=2.5000 CheapestPrice=9.2000 CheapestPrice=7.0000

Min - Elements

This sample uses Min to get the products with the cheapest price in each category.

C#

public void Linq84()
{
    List<Product> products = GetProductList();
 
    var categories =
        from p in products
        group p by p.Category into g
        let minPrice = g.Min(p => p.UnitPrice)
        select new { Category = g.Key, CheapestProducts = g.Where(p => p.UnitPrice == minPrice) };
 
    ObjectDumper.Write(categories, 1);
}

Result

Category=Beverages      CheapestProducts=...
  CheapestProducts: ProductID=24  ProductName=Guaraná Fantástica  Category=Beverages      UnitPrice=4.5000        UnitsInStock=20
Category=Condiments    CheapestProducts=...
  CheapestProducts: ProductID=3  ProductName=Aniseed Syrup      Category=Condiments    UnitPrice=10.0000      UnitsInStock=13
Category=Produce        CheapestProducts=...
  CheapestProducts: ProductID=74  ProductName=Longlife Tofu      Category=Produce        UnitPrice=10.0000      UnitsInStock=4
Category=Meat/Poultry  CheapestProducts=...
  CheapestProducts: ProductID=54  ProductName=Tourtière  Category=Meat/Poultry  UnitPrice=7.4500        UnitsInStock=21
Category=Seafood        CheapestProducts=...
  CheapestProducts: ProductID=13  ProductName=Konbu      Category=Seafood        UnitPrice=6.0000        UnitsInStock=24
Category=Dairy Products        CheapestProducts=...
  CheapestProducts: ProductID=33  ProductName=Geitost    Category=Dairy Products        UnitPrice=2.5000        UnitsInStock=112
Category=Confections    CheapestProducts=...
  CheapestProducts: ProductID=19  ProductName=Teatime Chocolate Biscuits  Category=Confections    UnitPrice=9.2000        UnitsInStock=25
Category=Grains/Cereals        CheapestProducts=...
  CheapestProducts: ProductID=52  ProductName=Filo Mix    Category=Grains/Cereals        UnitPrice=7.0000        UnitsInStock=38

Max - Simple

This sample uses Max to get the highest number in an array.

C#

public void Linq85()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
 
    int maxNum = numbers.Max();
 
    Console.WriteLine("The maximum number is {0}.", maxNum);
}

Result

The maximum number is 9.

Max - Projection

This sample uses Max to get the length of the longest word in an array.

C#

public void Linq86()
{
    string[] words = { "cherry", "apple", "blueberry" };
 
    int longestLength = words.Max(w => w.Length);
 
    Console.WriteLine("The longest word is {0} characters long.", longestLength);
}

Result

The longest word is 9 characters long.

Max - Grouped

This sample uses Max to get the most expensive price among each category's products.

C#

public void Linq87()
{
    List<Product> products = GetProductList();
 
    var categories =
        from p in products
        group p by p.Category into g
        select new { Category = g.Key, MostExpensivePrice = g.Max(p => p.UnitPrice) };
 
    ObjectDumper.Write(categories);
}

Result

Category=Beverages Category=Condiments Category=Produce Category=Meat/Poultry Category=Seafood Category=Dairy Products Category=Confections Category=Grains/Cereals

MostExpensivePrice=263.5000 MostExpensivePrice=43.9000 MostExpensivePrice=53.0000 MostExpensivePrice=123.7900 MostExpensivePrice=62.5000 MostExpensivePrice=55.0000 MostExpensivePrice=81.0000 MostExpensivePrice=38.0000

Max - Elements

This sample uses Max to get the products with the most expensive price in each category.

C#

public void Linq88()
{
    List<Product> products = GetProductList();
 
    var categories =
        from p in products
        group p by p.Category into g
        let maxPrice = g.Max(p => p.UnitPrice)
        select new { Category = g.Key, MostExpensiveProducts = g.Where(p => p.UnitPrice == maxPrice) };
 
    ObjectDumper.Write(categories, 1);
}

Result

Category=Beverages      MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=38    ProductName=Côte de Blaye      Category=Beverages      UnitPrice=263.5000      UnitsInStock=17
Category=Condiments    MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=63    ProductName=Vegie-spread        Category=Condiments    UnitPrice=43.9000      UnitsInStock=24
Category=Produce        MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=51    ProductName=Manjimup Dried Apples      Category=Produce        UnitPrice=53.0000      UnitsInStock=20
Category=Meat/Poultry  MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=29    ProductName=Thüringer Rostbratwurst    Category=Meat/Poultry  UnitPrice=123.7900      UnitsInStock=0
Category=Seafood        MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=18    ProductName=Carnarvon Tigers    Category=Seafood        UnitPrice=62.5000      UnitsInStock=42
Category=Dairy Products        MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=59    ProductName=Raclette Courdavault        Category=Dairy Products        UnitPrice=55.0000      UnitsInStock=79
Category=Confections    MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=20    ProductName=Sir Rodney's Marmalade      Category=Confections    UnitPrice=81.0000      UnitsInStock=40
Category=Grains/Cereals        MostExpensiveProducts=...
  MostExpensiveProducts: ProductID=56    ProductName=Gnocchi di nonna Alice      Category=Grains/Cereals        UnitPrice=38.0000      UnitsInStock=21

Average - Simple

This sample uses Average to get the average of all numbers in an array.

C#

public void Linq89()
{
    int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
 
    double averageNum = numbers.Average();
 
    Console.WriteLine("The average number is {0}.", averageNum);
}

Result

The average number is 4.5.

Average - Projection

This sample uses Average to get the average length of the words in the array.

C#

public void Linq90()
{
    string[] words = { "cherry", "apple", "blueberry" };
 
    double averageLength = words.Average(w => w.Length);
 
    Console.WriteLine("The average word length is {0} characters.", averageLength);
}

Result

The average word length is 6.66666666666667 characters.

Average - Grouped

This sample uses Average to get the average price of each category's products.

C#

public void Linq91()
{
    List<Product> products = GetProductList();
 
    var categories =
        from p in products
        group p by p.Category into g
        select new { Category = g.Key, AveragePrice = g.Average(p => p.UnitPrice) };
 
    ObjectDumper.Write(categories);
}

Result

Category=Beverages Category=Condiments Category=Produce Category=Meat/Poultry Category=Seafood Category=Dairy Products Category=Confections Category=Grains/Cereals

AveragePrice=37.979166666666666666666666667 AveragePrice=23.0625 AveragePrice=32.3700 AveragePrice=54.006666666666666666666666667 AveragePrice=20.6825 AveragePrice=28.7300 AveragePrice=25.1600 AveragePrice=20.2500

Aggregate - Simple

This sample uses Aggregate to create a running product on the array that calculates the total product of all elements.

C#

public void Linq92()
{
    double[] doubles = { 1.7, 2.3, 1.9, 4.1, 2.9 };
 
    double product = doubles.Aggregate((runningProduct, nextFactor) => runningProduct * nextFactor);
 
    Console.WriteLine("Total product of all numbers: {0}", product);
}

Result

Total product of all numbers: 88.33081

Aggregate - Seed

This sample uses Aggregate to create a running account balance that subtracts each withdrawal from the initial balance of 100, as long as the balance never drops below 0.

C#

public void Linq93()
{
    double startBalance = 100.0;
 
    int[] attemptedWithdrawals = { 20, 10, 40, 50, 10, 70, 30 };
 
    double endBalance =
        attemptedWithdrawals.Aggregate(startBalance,
            (balance, nextWithdrawal) =>
                ((nextWithdrawal <= balance) ? (balance - nextWithdrawal) : balance));
 
    Console.WriteLine("Ending balance: {0}", endBalance);
}

Result

Ending balance: 20