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Queryable.Distinct<TSource> Method (IQueryable<TSource>, IEqualityComparer<TSource>)

Returns distinct elements from a sequence by using a specified IEqualityComparer<T> to compare values.

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

public static IQueryable<TSource> Distinct<TSource>(
	this IQueryable<TSource> source,
	IEqualityComparer<TSource> comparer

Type Parameters


The type of the elements of source.


Type: System.Linq.IQueryable<TSource>

The IQueryable<T> to remove duplicates from.

Type: System.Collections.Generic.IEqualityComparer<TSource>

An IEqualityComparer<T> to compare values.

Return Value

Type: System.Linq.IQueryable<TSource>
An IQueryable<T> that contains distinct elements from source.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).


source or comparer is null.

The Distinct<TSource>(IQueryable<TSource>, IEqualityComparer<TSource>) method generates a MethodCallExpression that represents calling Distinct<TSource>(IQueryable<TSource>, IEqualityComparer<TSource>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling Distinct<TSource>(IQueryable<TSource>, IEqualityComparer<TSource>) depends on the implementation of the type of the source parameter. The expected behavior is that it returns an unordered sequence of the unique items in source by using comparer to compare values.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5