Enumerable.Count(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Boolean))
Returns a number that represents how many elements in the specified sequence satisfy a condition.
Assembly: System.Core (in System.Core.dll)
<ExtensionAttribute> Public Shared Function Count(Of TSource) ( source As IEnumerable(Of TSource), predicate As Func(Of TSource, Boolean) ) As Integer
Parameters
- source
-
Type:
System.Collections.Generic.IEnumerable(Of TSource)
A sequence that contains elements to be tested and counted.
- predicate
-
Type:
System.Func(Of TSource, Boolean)
A function to test each element for a condition.
Return Value
Type: System.Int32A number that represents how many elements in the sequence satisfy the condition in the predicate function.
Type Parameters
- TSource
The type of the elements of source.
| Exception | Condition |
|---|---|
| ArgumentNullException | source or predicate is null. |
| OverflowException | The number of elements in source is larger than MaxValue. |
If the type of source implements ICollection(Of T), that implementation is used to obtain the count of elements. Otherwise, this method determines the count.
You should use the LongCount(Of TSource) method when you expect and want to allow the result to be greater than MaxValue.
In Visual Basic query expression syntax, an Aggregate Into Count() clause translates to an invocation of Count.
The following code example demonstrates how to use Count(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Boolean)) to count the elements in an array that satisfy a condition.
Structure Pet Public Name As String Public Vaccinated As Boolean End Structure Public Shared Sub CountEx2() ' Create an array of Pet objects. Dim pets() As Pet = {New Pet With {.Name = "Barley", .Vaccinated = True}, New Pet With {.Name = "Boots", .Vaccinated = False}, New Pet With {.Name = "Whiskers", .Vaccinated = False}} Try ' Count the number of Pets in the array where the Vaccinated property is False. Dim numberUnvaccinated As Integer = pets.Count(Function(p) p.Vaccinated = False) ' Display the output. MsgBox("There are " & numberUnvaccinated & " unvaccinated animals.") Catch e As OverflowException MsgBox("The count is too large to store as an Int32. Try using LongCount() instead.") End Try End Sub ' This code produces the following output: ' ' There are 2 unvaccinated animals.
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 7.0
Windows Phone
Available since 8.1