Enumerable.​Count Method

Definition

Overloads

Count<​TSource>(​IEnumerable<​TSource>)

Returns the number of elements in a sequence.

Count<​TSource>(​IEnumerable<​TSource>, ​Func<​TSource,​Boolean>)

Returns a number that represents how many elements in the specified sequence satisfy a condition.

Count<TSource>(IEnumerable<TSource>)

Returns the number of elements in a sequence.

public static int Count<TSource> (this System.Collections.Generic.IEnumerable<TSource> source);
Type Parameters
TSource

The type of the elements of source.

Parameters
source
IEnumerable<TSource>

A sequence that contains elements to be counted.

Returns

The number of elements in the input sequence.

Exceptions

source is null.

The number of elements in source is larger than MaxValue.

Examples

The following code example demonstrates how to use Count<TSource>(IEnumerable<TSource>) to count the elements in an array.

string[] fruits = { "apple", "banana", "mango", "orange", "passionfruit", "grape" };

try
{
    int numberOfFruits = fruits.Count();
    Console.WriteLine(
        "There are {0} fruits in the collection.",
        numberOfFruits);

}
catch (OverflowException)
{
    Console.WriteLine("The count is too large to store as an Int32.");
    Console.WriteLine("Try using the LongCount() method instead.");
}

// This code produces the following output:
//
// There are 6 fruits in the collection. 

' Create an array of strings.
Dim fruits() As String = {"apple", "banana", "mango", "orange", "passionfruit", "grape"}

Try
    ' Count the number of items in the array.
    Dim numberOfFruits As Integer = fruits.Count()
    ' Display the output.
    MsgBox("There are " & numberOfFruits & " fruits in the collection.")
Catch e As OverflowException
    MsgBox("The count is too large to store as an Int32. Try using LongCount() instead.")
End Try

' This code produces the following output:
'
' There are 6 fruits in the collection.

Remarks

If the type of source implements ICollection<T>, that implementation is used to obtain the count of elements. Otherwise, this method determines the count.

Use the LongCount 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.

Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>)

Returns a number that represents how many elements in the specified sequence satisfy a condition.

public static int Count<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,bool> predicate);
Type Parameters
TSource

The type of the elements of source.

Parameters
source
IEnumerable<TSource>

A sequence that contains elements to be tested and counted.

predicate
Func<TSource,Boolean>

A function to test each element for a condition.

Returns

A number that represents how many elements in the sequence satisfy the condition in the predicate function.

Exceptions

source or predicate is null.

The number of elements in source is larger than MaxValue.

Examples

The following code example demonstrates how to use Count<TSource>(IEnumerable<TSource>, Func<TSource,Boolean>) to count the elements in an array that satisfy a condition.

class Pet
{
    public string Name { get; set; }
    public bool Vaccinated { get; set; }
}

public static void CountEx2()
{
    Pet[] pets = { new Pet { Name="Barley", Vaccinated=true },
                   new Pet { Name="Boots", Vaccinated=false },
                   new Pet { Name="Whiskers", Vaccinated=false } };

    try
    {
        int numberUnvaccinated = pets.Count(p => p.Vaccinated == false);
        Console.WriteLine("There are {0} unvaccinated animals.", numberUnvaccinated);
    }
    catch (OverflowException)
    {
        Console.WriteLine("The count is too large to store as an Int32.");
        Console.WriteLine("Try using the LongCount() method instead.");
    }
}

// This code produces the following output:
//
// There are 2 unvaccinated animals.

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.

Remarks

If the type of source implements ICollection<T>, that implementation is used to obtain the count of elements. Otherwise, this method determines the count.

You should use the LongCount 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.