System.Linq Namespace

Provides classes and interfaces that support LINQ (Language-Integrated Query), which adds querying capabilities to .NET languages. These capabilities are primarily used for querying collections of objects, XML documents, databases, and other data sources.

Classes

Class

Enumerable

Represents a queryable collection of elements of a specified type. This is the primary entry point for LINQ to Objects queries.

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public static class Enumerable
Class

Queryable

Provides static methods that support the creation and execution of IQueryable<T> objects. This is the primary entry point for LINQ to providers such as LINQ to SQL or LINQ to Entities.

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public static class Queryable

Interfaces

Interface

IEnumerable<T>

Supports iteration over a non-generic collection of objects. It is the base interface for all LINQ queries.

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public interface IEnumerable<out T> : IEnumerable
Interface

IQueryable<T>

Represents a query that can be executed. It is the base interface for LINQ providers.

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public interface IQueryable<out T> : IEnumerable<T>, IQueryable
Interface

IGrouping<TKey, TElement>

Represents a group of elements that have a common key. Used in group by operations.

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

Extension Methods (from Enumerable)

Extension Method

Where<TSource>

Filters a sequence of values based on a predicate.

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public static IEnumerable<TSource> Where<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate)
Extension Method

Select<TSource, TResult>

Projects each element of a sequence into a new form.

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public static IEnumerable<TResult> Select<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> selector)
Extension Method

OrderBy<TSource, TKey>

Sorts the elements of a sequence in ascending order according to a key.

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public static IOrderedEnumerable<TSource> OrderBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
Extension Method

GroupBy<TSource, TKey>

Groups the elements of a sequence based on a specified key selector function.

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public static IEnumerable<IGrouping<TKey, TSource>> GroupBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)