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

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

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

public static int Count<TSource>(
	this IEnumerable<TSource> source,
	Func<TSource, bool> predicate

Type Parameters


The type of the elements of source.


Type: System.Collections.Generic.IEnumerable<TSource>
A sequence that contains elements to be tested and counted.
Type: System.Func<TSource, Boolean>
A function to test each element for a condition.

Return Value

Type: System.Int32
A number that represents how many elements in the sequence satisfy the condition in the predicate function.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter.


source or predicate is null.


The number of elements in source is larger than MaxValue.

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.

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(System.Windows.Controls.TextBlock outputBlock)
         Pet[] pets = { new Pet { Name="Barley", Vaccinated=true },
                            new Pet { Name="Boots", Vaccinated=false },
                            new Pet { Name="Whiskers", Vaccinated=false } };

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

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


Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.