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Enumerable.Where<TSource> Method (IEnumerable<TSource>, Func<TSource, Int32, Boolean>)


Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

public static IEnumerable<TSource> Where<TSource>(
	this IEnumerable<TSource> source,
	Func<TSource, intbool> predicate


Type: System.Collections.Generic.IEnumerable<TSource>

An IEnumerable<T> to filter.

Type: System.Func<TSourceInt32Boolean>

A function to test each source element for a condition; the second parameter of the function represents the index of the source element.

Return Value

Type: System.Collections.Generic.IEnumerable<TSource>

An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.

Type Parameters


The type of the elements of source.

Exception Condition

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.

The first argument of predicate represents the element to test. The second argument represents the zero-based index of the element within source.

The following code example demonstrates how to use Where<TSource>(IEnumerable<TSource>, Func<TSource, Int32, Boolean>) to filter a sequence based on a predicate that involves the index of each element.

int[] numbers = { 0, 30, 20, 15, 90, 85, 40, 75 };

IEnumerable<int> query =
    numbers.Where((number, index) => number <= index * 10);

foreach (int number in query)
 This code produces the following output:


Universal Windows Platform
Available since 4.5
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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