System.Linq Namespace

The System.Linq namespace provides classes and interfaces that support queries that use Language-Integrated Query (LINQ).

Classes

Enumerable	Provides a set of `static` (`Shared` in Visual Basic) methods for querying objects that implement IEnumerable<T>.
EnumerableExecutor	Represents an expression tree and provides functionality to execute the expression tree after rewriting it.
EnumerableExecutor<T>	Represents an expression tree and provides functionality to execute the expression tree after rewriting it.
EnumerableQuery	Represents an IEnumerable as an EnumerableQuery data source.
EnumerableQuery<T>	Represents an IEnumerable<T> collection as an IQueryable<T> data source.
ImmutableArrayExtensions	LINQ extension method overrides that offer greater efficiency for ImmutableArray<T> than the standard LINQ methods NuGet package: System.Collections.Immutable (about immutable collections and how to install)
Lookup<TKey,TElement>	Represents a collection of keys each mapped to one or more values.
OrderedParallelQuery<TSource>	Represents a sorted, parallel sequence.
ParallelEnumerable	Provides a set of methods for querying objects that implement ParallelQuery{TSource}. This is the parallel equivalent of Enumerable.
ParallelQuery	Represents a parallel sequence.
ParallelQuery<TSource>	Represents a parallel sequence.
Queryable	Provides a set of `static` (`Shared` in Visual Basic) methods for querying data structures that implement IQueryable<T>.

IGrouping<TKey,TElement>	Represents a collection of objects that have a common key.
ILookup<TKey,TElement>	Defines an indexer, size property, and Boolean search method for data structures that map keys to IEnumerable<T> sequences of values.
IOrderedEnumerable<TElement>	Represents a sorted sequence.
IOrderedQueryable	Represents the result of a sorting operation.
IOrderedQueryable<T>	Represents the result of a sorting operation.
IQueryable	Provides functionality to evaluate queries against a specific data source wherein the type of the data is not specified.
IQueryable<T>	Provides functionality to evaluate queries against a specific data source wherein the type of the data is known.
IQueryProvider	Defines methods to create and execute queries that are described by an IQueryable object.

ParallelExecutionMode	The query execution mode is a hint that specifies how the system should handle performance trade-offs when parallelizing queries.
ParallelMergeOptions	Specifies the preferred type of output merge to use in a query. In other words, it indicates how PLINQ should merge the results from the various partitions back into a single result sequence. This is a hint only, and may not be respected by the system when parallelizing all queries.

The System.Linq namespace is in the System.Core assembly (in System.Core.dll).

The Enumerable class contains LINQ standard query operators that operate on objects that implement IEnumerable<T>.

The Queryable class contains LINQ standard query operators that operate on objects that implement IQueryable<T>.

For information about LINQ to SQL, see LINQ to SQL [LINQ to SQL].