Observable.Where<TSource> Method (IObservable<TSource>, Func<TSource, Boolean>)
Filters the elements of an observable sequence based on a predicate.
Namespace: System.Reactive.Linq
Assembly: System.Reactive (in System.Reactive.dll)
Syntax
'Declaration
<ExtensionAttribute> _
Public Shared Function Where(Of TSource) ( _
source As IObservable(Of TSource), _
predicate As Func(Of TSource, Boolean) _
) As IObservable(Of TSource)
'Usage
Dim source As IObservable(Of TSource)
Dim predicate As Func(Of TSource, Boolean)
Dim returnValue As IObservable(Of TSource)
returnValue = source.Where(predicate)
public static IObservable<TSource> Where<TSource>(
this IObservable<TSource> source,
Func<TSource, bool> predicate
)
[ExtensionAttribute]
public:
generic<typename TSource>
static IObservable<TSource>^ Where(
IObservable<TSource>^ source,
Func<TSource, bool>^ predicate
)
static member Where :
source:IObservable<'TSource> *
predicate:Func<'TSource, bool> -> IObservable<'TSource>
JScript does not support generic types and methods.
Type Parameters
- TSource
The type source.
Parameters
- source
Type: System.IObservable<TSource>
An observable sequence whose elements to filter.
- predicate
Type: System.Func<TSource, Boolean>
A function to test each source element for a condition.
Return Value
Type: System.IObservable<TSource>
An observable sequence 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 IObservable<TSource>. When you use instance method syntax to call this method, omit the first parameter. For more information, see or .
Remarks
The Where operator allows you to define a predicate function to test each item in a sequence. Each item from the source sequence which causes the predicate function to return false is filtered from the resulting sequence.
Examples
The following example uses the Where operator with a Language Integerated Query (LINQ) to filter the integer sequence so that only even integers are produced for the sequence.
using System;
using System.Reactive.Linq;
namespace Example
{
class Program
{
static void Main()
{
//*********************************************************************************************//
//*** The mainSequence produces a new long integer from the Interval operator every sec. ***//
//*********************************************************************************************//
var mainSequence = Observable.Interval(TimeSpan.FromSeconds(1));
//*********************************************************************************************//
//*** This LINQ statement uses the Where operator to filter the integers in the sequence so ***//
//*** that only the even integers are returned. ***//
//*** ***//
//*** you could also call the method explicitly. For example... ***//
//*** ***//
//*** var seqWhereEven = mainSequence.Where(x => x % 2 == 0); ***//
//*** ***//
//*********************************************************************************************//
var seqWhereEven = from i in mainSequence
where i % 2 == 0
select i;
//*********************************************************************************************//
//*** Create a subscription and write each of the even integers to the console window. ***//
//*********************************************************************************************//
seqWhereEven.Subscribe(x => Console.WriteLine(x));
Console.ReadLine();
}
}
}
The following output was generated by the example code.
0
2
4
6
8
10
12
14
16