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Enumerable.Distinct<TSource> Method (IEnumerable<TSource>)

April 12, 2014

Returns distinct elements from a sequence by using the default equality comparer to compare values.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)
public static IEnumerable<TSource> Distinct<TSource>(
	this IEnumerable<TSource> source
)

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>
The sequence to remove duplicate elements from.

Return Value

Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> that contains distinct elements from the source sequence.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter.
ExceptionCondition
ArgumentNullException

source is null.

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.

The Distinct<TSource>(IEnumerable<TSource>) method returns an unordered sequence that contains no duplicate values. It uses the default equality comparer, Default, to compare values.

In Visual Basic query expression syntax, a Distinct clause translates to an invocation of Distinct.

The default equality comparer, Default, is used to compare values of the types that implement the IEqualityComparer<T> generic interface. To compare a custom data type, you need to implement this interface and provide your own GetHashCode and Equals methods for the type.

The following code example demonstrates how to use Distinct<TSource>(IEnumerable<TSource>) to return distinct elements from a sequence of integers.


      List<int> ages = new List<int> { 21, 46, 46, 55, 17, 21, 55, 55 };

      IEnumerable<int> distinctAges = ages.Distinct();

      outputBlock.Text += "Distinct ages:" + "\n";

      foreach (int age in distinctAges)
      {
         outputBlock.Text += age + "\n";
      }

      /*
       This code produces the following output:

       Distinct ages:
       21
       46
       55
       17
      */



If you want to return distinct elements from sequences of objects of some custom data type, you have to implement the IEqualityComparer<T> generic interface in the class.

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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