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Queryable.Select<TSource, TResult> Method (IQueryable<TSource>, Expression<Func<TSource, TResult>>)

Projects each element of a sequence into a new form.

Namespace:  System.Linq
Assemblies:   System.Linq.Queryable (in System.Linq.Queryable.dll)
  System.Core (in System.Core.dll)

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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).

ExceptionCondition
ArgumentNullException

source or selector is null.

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.

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

            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)
                Console.WriteLine(num);

            /*
                This code produces the following output:

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

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8
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