C# List Contains & Exists

last modified July 5, 2023

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

Source

List class - language reference

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

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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