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C# List Contains & Exists

last modified October 31, 2022

In this article we show how to check if an element or specific elements are in a list in C#.

C# list is a collection of elements of the same type. The elements can be accessed by index.

The basic two methods that check the existence of an element or elements in a list are: Contains and Exists.

Alternatively, it is also possible to use Count, IndexOf, Find, or Any methods.

C# List Contains

The Contains method checks if an element is present in the list.

public bool Contains (T item);

The method returns a boolean value.

Program.cs
var words = new List<string> { "falcon", "water", "war", "pen", "ocean" };

var w1 = "war";
var w2 = "cup";

if (words.Contains(w1))
{
    Console.WriteLine($"{w1} is in the list");
}
else
{
    Console.WriteLine($"{w1} is not in the list");
}

if (words.Contains(w2))
{
    Console.WriteLine($"{w2} is in the list");
}
else
{
    Console.WriteLine($"{w2} is not in the list");
}

In the example, we check if two words are present in the list of defined words.

$ dotnet run
war is in the list
cup is not in the list

C# List Exists

The Exists method determines whether a list contains elements that match the specified predicate.

Program.cs
var words = new List<string> { "falcon", "water", "war", "pen", "ocean" };

bool res = words.Exists(e => e.StartsWith("w"));

if (res)
{
    Console.WriteLine("There are words starting in w");
} else
{
    Console.WriteLine("There are no words starting in w");
}


bool res2 = words.Exists(e => e.EndsWith("c"));

if (res2)
{
    Console.WriteLine("There are words ending in c");
} else
{
    Console.WriteLine("There are no words ending in c");
}

In the program we check if there are some words starting in 'w' and ending in 'c';

bool res = words.Exists(e => e.StartsWith("w"));

The Exists method takes a predicate function as a parameter. The predicate is in the form of lambda expression.

if (res)
{
    Console.WriteLine("There are words starting in w");
} else
{
    Console.WriteLine("There are no words starting in w");
}

A message is printed based on the received value.

$ dotnet run
There are words starting in w
There are no words ending in c

C# Enumerable.Count

We can check the existence of an element or elements in a list with LINQ's Count. The Count method returns the number of elements in a sequence.

There are two overloaded Count methods. One counts all the elements, the other one counts all the elements that match a condition.

Program.cs
var vals = new List<int> { -2, 0, -1, 4, 3, 5, 3, 8 };

int n = vals.Count(e => e < 0);

if (n == 0)
{
    Console.WriteLine("There are no negative values");
} else 
{
    Console.WriteLine($"There are {n} negative values");
}

In the program we check if there are negative values in a list with Count.

int n = vals.Count(e => e < 0);

We use the method that takes a predicate as a parameter.

$ dotnet run
There are 2 negative values

C# Enumerable.Any

The Any method determines whether any element of a sequence exists or satisfies a condition. It returns a boolean true or false.

Program.cs
var vals = new List<int> { -2, 0, -1, 4, 3, 5, 3, 8 };

bool r = vals.Any(e => e < 0);

if (r)
{
    Console.WriteLine("There are negative values");
} else 
{
    Console.WriteLine($"There are no negative values");
}

In the program we check if there are some negative values with Any.

$ dotnet run
There are negative values

In this article, we have showed how to check if an element in present in a list in C#.

List all C# tutorials.