Enumerable.Where Method
Definition
Important
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Filters a sequence of values based on a predicate.
Overloads
| Where<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) |
Filters a sequence of values based on a predicate. |
| Where<TSource>(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. |
Where<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)
- Source:
- Where.cs
- Source:
- Where.cs
- Source:
- Where.cs
Filters a sequence of values based on a predicate.
public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static System::Collections::Generic::IEnumerable<TSource> ^ Where(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, bool> ^ predicate);public static System.Collections.Generic.IEnumerable<TSource> Where<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,bool> predicate);static member Where : seq<'Source> * Func<'Source, bool> -> seq<'Source><Extension()>
Public Function Where(Of TSource) (source As IEnumerable(Of TSource), predicate As Func(Of TSource, Boolean)) As IEnumerable(Of TSource)Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
- IEnumerable<TSource>
An IEnumerable<T> to filter.
Returns
An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.
Exceptions
source or predicate is null.
Examples
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
*/
' Create a list of strings.
Dim fruits As New List(Of String)(New String() _
{"apple", "passionfruit", "banana", "mango",
"orange", "blueberry", "grape", "strawberry"})
' Restrict the results to those strings whose
' length is less than six.
Dim query As IEnumerable(Of String) =
fruits.Where(Function(fruit) fruit.Length < 6)
' Display the results.
Dim output As New System.Text.StringBuilder
For Each fruit As String In query
output.AppendLine(fruit)
Next
Console.WriteLine(output.ToString())
' This code produces the following output:
'
' apple
' mango
' grape
Remarks
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 C# or For Each in Visual Basic.
In query expression syntax, a where (C#) or Where (Visual Basic) clause translates to an invocation of Where<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>).
See also
Applies to
Where<TSource>(IEnumerable<TSource>, Func<TSource,Int32,Boolean>)
- Source:
- Where.cs
- Source:
- Where.cs
- Source:
- Where.cs
Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function.
public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static System::Collections::Generic::IEnumerable<TSource> ^ Where(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, int, bool> ^ predicate);public static System.Collections.Generic.IEnumerable<TSource> Where<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,int,bool> predicate);static member Where : seq<'Source> * Func<'Source, int, bool> -> seq<'Source><Extension()>
Public Function Where(Of TSource) (source As IEnumerable(Of TSource), predicate As Func(Of TSource, Integer, Boolean)) As IEnumerable(Of TSource)Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
- IEnumerable<TSource>
An IEnumerable<T> to filter.
A function to test each source element for a condition; the second parameter of the function represents the index of the source element.
Returns
An IEnumerable<T> that contains elements from the input sequence that satisfy the condition.
Exceptions
source or predicate is null.
Examples
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)
{
Console.WriteLine(number);
}
/*
This code produces the following output:
0
20
15
40
*/
' Create an array of integers.
Dim numbers() As Integer = {0, 30, 20, 15, 90, 85, 40, 75}
' Restrict the results to those numbers whose
' values are less than or equal to their index times 10.
Dim query As IEnumerable(Of Integer) =
numbers.Where(Function(number, index) number <= index * 10)
' Display the results.
Dim output As New System.Text.StringBuilder
For Each number As Integer In query
output.AppendLine(number)
Next
Console.WriteLine(output.ToString())
' This code produces the following output:
'
' 0
' 20
' 15
' 40
Remarks
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 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.
