Enumerable.Where<TSource> Method (IEnumerable<TSource>, Func<TSource, Boolean>)
Filters a sequence of values based on a predicate.
Assembly: System.Core (in System.Core.dll)
public static IEnumerable<TSource> Where<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate )
Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
- Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> to filter.
- predicate
- Type: System.Func<TSource, Boolean>
A function to test each element for a condition.
Return Value
Type: System.Collections.Generic.IEnumerable<TSource>An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.
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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).| Exception | Condition |
|---|---|
| ArgumentNullException |
source or predicate is null. |
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.
In query expression syntax, a where (Visual C#) or Where (Visual Basic) clause translates to an invocation of Where<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>).
The following code example demonstrates how to use Where<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) to filter a sequence.
List<string> fruits =
new List<string> { "apple", "passionfruit", "banana", "mango",
"orange", "blueberry", "grape", "strawberry" };
IEnumerable<string> query = fruits.Where(fruit => fruit.Length < 6);
foreach (string fruit in query)
{
Console.WriteLine(fruit);
}
/*
This code produces the following output:
apple
mango
grape
*/
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
using namespace System;
using namespace System::Collections::Generic;
using namespace System::Linq;
public ref class CWhereHelper
{
public:
static bool LenLtSix(String^ str)
{
return str->Length < 6;
}
static Func<String^, bool>^ lenLtSix = gcnew Func<String^, bool>(LenLtSix);
static void DoWhere()
{
List<String^>^ fruits =
gcnew List<String^>(gcnew array<String^> {
"apple", "passionfruit", "banana", "mango",
"orange", "blueberry", "grape", "strawberry" });
IEnumerable<String^>^ query = Enumerable::Where(fruits, lenLtSix);
for each(String^ fruit in query)
{
Console::WriteLine(fruit);
}
/*
This code produces the following output:
apple
mango
grape
*/
}
};
- 2/13/2012
- THines01
