Queryable.Select<TSource, TResult> Method (IQueryable<TSource>, Expression<Func<TSource, TResult>>)
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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 IQueryable(Of TSource), _
selector As Expression(Of Func(Of TSource, TResult)) _
) As IQueryable(Of TResult)
public static IQueryable<TResult> Select<TSource, TResult>(
this IQueryable<TSource> source,
Expression<Func<TSource, TResult>> selector
)
Type Parameters
- TSource
The type of the elements of source.
- TResult
The type of the value returned by the function represented by selector.
Parameters
- source
Type: System.Linq.IQueryable<TSource>
A sequence of values to project.
- selector
Type: System.Linq.Expressions.Expression<Func<TSource, TResult>>
A projection function to apply to each element.
Return Value
Type: System.Linq.IQueryable<TResult>
An IQueryable<T> whose elements are the result of invoking a projection 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 IQueryable<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 has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T, TResult> types. For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.
The Select<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, TResult>>) method generates a MethodCallExpression that represents calling Select<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, TResult>>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery(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 Select<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, TResult>>) depends on the implementation of the type of the source parameter. The expected behavior is that it invokes selector on each element of source to project it into a different form.
Examples
The following code example demonstrates how to use Select<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, TResult>>) to project over a sequence of values.
Dim range As New List(Of Integer)(New Integer() {1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
' Project the square of each int value.
Dim squares As IEnumerable(Of Integer) = _
range.AsQueryable().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
List<int> range =
new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
// Project the square of each int value.
IEnumerable<int> squares =
range.AsQueryable().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
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.