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Enumerable.Select(Of TSource, TResult) Method (IEnumerable(Of TSource), Func(Of TSource, TResult))

April 12, 2014

Projects each element of a sequence into a new form.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)
'Déclaration
<ExtensionAttribute> _
Public Shared Function Select(Of TSource, TResult) ( _
	source As IEnumerable(Of TSource), _
	selector As Func(Of TSource, TResult) _
) As IEnumerable(Of TResult)

Type Parameters

TSource

The type of the elements of source.

TResult

The type of the value returned by selector.

Parameters

source
Type: System.Collections.Generic.IEnumerable(Of TSource)
A sequence of values to invoke a transform function on.
selector
Type: System.Func(Of TSource, TResult)
A transform function to apply to each element.

Return Value

Type: System.Collections.Generic.IEnumerable(Of TResult)
An IEnumerable(Of 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(Of TSource). When you use instance method syntax to call this method, omit the first parameter.
ExceptionCondition
ArgumentNullException

source or selector is Nothing.

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 Enumerable.Select.

The following code example demonstrates how to use Select(Of TSource, TResult)(IEnumerable(Of TSource), Func(Of 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



Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

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