Export (0) Print
Expand All

Enumerable.Empty<TResult> Method

Returns an empty IEnumerable<T> that has the specified type argument.

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

public static IEnumerable<TResult> Empty<TResult>()

Type Parameters

TResult

The type to assign to the type parameter of the returned generic IEnumerable<T>.

Return Value

Type: System.Collections.Generic.IEnumerable<TResult>
An empty IEnumerable<T> whose type argument is TResult.

The Empty<TResult>() method caches an empty sequence of type TResult. When the object it returns is enumerated, it yields no elements.

In some cases, this method is useful for passing an empty sequence to a user-defined method that takes an IEnumerable<T>. It can also be used to generate a neutral element for methods such as Union. See the Example section for an example of this use of Empty<TResult>().

The following code example demonstrates how to use Empty<TResult>() to generate an empty IEnumerable<T>.


IEnumerable<decimal> empty = Enumerable.Empty<decimal>();


The following code example demonstrates a possible application of the Empty<TResult>() method. The Aggregate method is applied to a collection of string arrays. The elements of each array in the collection are added to the resulting IEnumerable<T> only if that array contains four or more elements. Empty<TResult> is used to generate the seed value for Aggregate because if no array in the collection has four or more elements, only the empty sequence is returned.


      string[] names1 = { "Hartono, Tommy" };
      string[] names2 = { "Adams, Terry", "Andersen, Henriette Thaulow",
                               "Hedlund, Magnus", "Ito, Shu" };
      string[] names3 = { "Solanki, Ajay", "Hoeing, Helge",
                               "Andersen, Henriette Thaulow",
                               "Potra, Cristina", "Iallo, Lucio" };

      List<string[]> namesList =
          new List<string[]> { names1, names2, names3 };

      // Only include arrays that have four or more elements
      IEnumerable<string> allNames =
          namesList.Aggregate(Enumerable.Empty<string>(),
          (current, next) => next.Length > 3 ? current.Union(next) : current);

      foreach (string name in allNames)
      {
         outputBlock.Text += name + "\n";
      }

      /*
       This code produces the following output:

       Adams, Terry
       Andersen, Henriette Thaulow
       Hedlund, Magnus
       Ito, Shu
       Solanki, Ajay
       Hoeing, Helge
       Potra, Cristina
       Iallo, Lucio
      */



Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Community Additions

ADD
Show:
© 2015 Microsoft