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Enumerable.Select<TSource, TResult> Method (IEnumerable<TSource>, Func<TSource, TResult>)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Projects each element of a sequence into a new form.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Select(Of TSource, TResult) ( _
    source As IEnumerable(Of TSource), _
    selector As Func(Of TSource, TResult) _
) As IEnumerable(Of TResult)

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

Type Parameters

  • TSource
    The type of the elements of source.
  • TResult
    The type of the value returned by selector.

Parameters

  • selector
    Type: System.Func<TSource, TResult>
    A transform function to apply to each element.

Return Value

Type: System.Collections.Generic.IEnumerable<TResult>
An IEnumerable<T> whose elements are the result of invoking the transform function on each element of source.

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.

Exceptions

Exception Condition
ArgumentNullException

source or selector is nulla null reference (Nothing in Visual Basic).

Remarks

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.

This projection method requires the transform function, selector, to produce one value for each value in the source sequence, source. If selector returns a value that is itself a collection, it is up to the consumer to traverse the subsequences manually. In such a situation, it might be better for your query to return a single coalesced sequence of values. To achieve this, use the SelectMany method instead of Select. Although SelectMany works similarly to Select, it differs in that the transform function returns a collection that is then expanded by SelectMany before it is returned.

In query expression syntax, a select (Visual C#) or Select (Visual Basic) clause translates to an invocation of Select.

Examples

The following code example demonstrates how to use Select<TSource, TResult>(IEnumerable<TSource>, Func<TSource, TResult>) to project over a sequence of values.

      ' Create a collection of sequential integers
      ' from 1 to 10 and project their squares.
      Dim squares As IEnumerable(Of Integer) = _
          Enumerable.Range(1, 10).Select(Function(x) x * x)

      Dim output As New System.Text.StringBuilder
      For Each num As Integer In squares
         output.AppendLine(num)
      Next

      ' Display the output.
      outputBlock.Text &= output.ToString() & vbCrLf

      ' This code produces the following output:
      '
      ' 1
      ' 4
      ' 9
      ' 16
      ' 25
      ' 36
      ' 49
      ' 64
      ' 81
      ' 100


      IEnumerable<int> squares =
          Enumerable.Range(1, 10).Select(x => x * x);

      foreach (int num in squares)
      {
         outputBlock.Text += num + "\n";
      }
      /*
       This code produces the following output:

       1
       4
       9
       16
       25
       36
       49
       64
       81
       100
      */

Version Information

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

Platforms

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