Queryable.Select<TSource, TResult> Method (IQueryable<TSource>, Expression<Func<TSource, Int32, TResult>>)
Projects each element of a sequence into a new form by incorporating the element's index.
Assembly: System.Core (in System.Core.dll)
public static IQueryable<TResult> Select<TSource, TResult>( this IQueryable<TSource> source, Expression<Func<TSource, int, TResult>> selector )
Parameters
- source
-
Type:
System.Linq.IQueryable<TSource>
A sequence of values to project.
- selector
-
Type:
System.Linq.Expressions.Expression<Func<TSource, Int32, 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.
Type Parameters
- TSource
The type of the elements of source.
- TResult
The type of the value returned by the function represented by selector.
| Exception | Condition |
|---|---|
| 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, Int32, TResult>>) method generates a MethodCallExpression that represents calling Select<TSource, TResult>(IQueryable<TSource>, Expression<Func<TSource, Int32, 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, Int32, TResult>>) depend 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, Int32, TResult>>) to project over a sequence of values and use the index of each element in the projected form.
string[] fruits = { "apple", "banana", "mango", "orange", "passionfruit", "grape" }; // Project an anonymous type that contains the // index of the string in the source array, and // a string that contains the same number of characters // as the string's index in the source array. var query = fruits.AsQueryable() .Select((fruit, index) => new { index, str = fruit.Substring(0, index) }); foreach (var obj in query) Console.WriteLine("{0}", obj); /* This code produces the following output: { index = 0, str = } { index = 1, str = b } { index = 2, str = ma } { index = 3, str = ora } { index = 4, str = pass } { index = 5, str = grape } */
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1