C# filter list
last modified June 8, 2025
In this article, we explore different techniques for filtering a list in C#. Whether you're working with large datasets or optimizing search functionality, understanding efficient filtering methods is essential.
This tutorial covers multiple approaches to filtering lists in C#, including
iteration, LINQ queries, and the built-in FindAll and
RemoveAll methods.
C# filter list with iteration
In the first example, we use a foreach loop to filter a list.
List<string> words = [ "sky", "rock", "forest", "new",
"falcon", "jewelry" ];
List<string> filtered = [];
foreach (var word in words)
{
if (word.Length == 3)
{
filtered.Add(word);
}
}
Console.WriteLine(string.Join(',', filtered));
The example filters out all words that have three characters.
List<string> words = [ "sky", "rock", "forest", "new",
"falcon", "jewelry" ];
We have a list of words. The goal is to find out all words with three letters.
List<string> filtered = [];
A new filtered list is created. All the words that match the
condition will be added to the list.
foreach (var word in words)
{
if (word.Length == 3)
{
filtered.Add(word);
}
}
We go over the list of words in a foreach loop. All words that
match the if condition are added to the filtered list.
Console.WriteLine(string.Join(',', filtered));
We show the contents of the filtered list to the console.
$ dotnet run sky,new
C# filter list with FindAll
In the following example, we filter a list with the built-in FindAll
method.
List<int> vals = [-1, -3, 0, 1, 3, 2, 9, -4];
List<int> filtered = vals.FindAll(e => e > 0);
Console.WriteLine(string.Join(',', filtered));
The example finds out all integer values that are greater than zero.
List<int> filtered = vals.FindAll(e => e > 0);
The FindAll method retrieves all the elements that match the
conditions defined by the specified predicate.
$ dotnet run 1,3,2,9
C# filter list with LINQ query expression
The following example uses a LINQ query expression to filter a list.
List<string> words = [ "sky", "rock", "forest", "new",
"falcon", "jewelry" ];
var query = from word in words
where word.Length == 3
select word;
foreach (var word in query)
{
Console.WriteLine(word);
}
The example selects all words that have three characters. The where
clause filters the words based on the specified condition, while the
select clause specifies the elements to be returned.
C# filter list with LINQ Where
The next example filters a list with LINQ's Where method.
It is a more concise way to filter collections compared to using a
foreach loop or the FindAll method. It takes a
predicate function that defines the filtering condition and returns a new
list containing only the elements that satisfy the condition.
List<int> vals = [-1, -3, 0, 1, 3, 2, 9, -4];
List<int> filtered = vals.Where(x => x > 0).ToList();
Console.WriteLine(string.Join(',', filtered));
The example filters out all positive values.
List<int> filtered = vals.Where(x => x > 0).ToList();
The Where method filters a sequence of values based on a predicate.
C# filter a list of objects
In the following example we filter a list of car objects with a LINQ query expression.
List<Car> cars =
[
new ("Audi", 52642),
new ("Mercedes", 57127),
new ("Skoda", 9000),
new ("Volvo", 29000),
new ("Bentley", 350000),
new ("Citroen", 21000),
new ("Hummer", 41400),
new ("Volkswagen", 21601)
];
foreach (var car in from car in cars
where car.Price > 9000 && car.Price < 50000
select new { car.Name, car.Price })
{
Console.WriteLine($"{car.Name} {car.Price}");
}
record Car(string Name, int Price);
The example selects all cars whose price is between 9000 and 50000.
$ dotnet run Volvo 29000 Citroen 21000 Hummer 41400 Volkswagen 21600
C# filter List with Func
In the example, we use a Func delegate to filter a list of users.
This approach allows us to define a predicate function that can be reused
for filtering based on different criteria. The Func delegate
represents a method that takes a single parameter and returns a boolean value,
making it suitable for use with LINQ methods like Where.
List<User> users =
[
new (1, "John", "London", "2001-04-01"),
new (2, "Lenny", "New York", "1997-12-11"),
new (3, "Andrew", "Boston", "1987-02-22"),
new (4, "Peter", "Prague", "1936-03-24"),
new (5, "Anna", "Bratislava", "1973-11-18"),
new (6, "Albert", "Bratislava", "1940-12-11"),
new (7, "Adam", "Trnava", "1983-12-01"),
new (8, "Robert", "Bratislava", "1935-05-15"),
new (9, "Robert", "Prague", "1998-03-14"),
];
var city = "Bratislava";
Func<User, bool> livesIn = e => e.City == city;
var res = users.Where(livesIn);
foreach (var e in res)
{
Console.WriteLine(e);
}
record User(int Id, string Name, string City, string DateOfBirth);
From the array of users, we get those that live in Bratislava.
var city = "Bratislava"; Func<User, bool> livesIn = e => e.City == city;
In the predicate, a function which returns a boolean value, we test all user
objects whose City attribute is equal to the city
variable.
var res = users.Where(livesIn);
We pass the livesIn predicate to the Where method.
$ dotnet run
User { Id = 5, Name = Anna, City = Bratislava, DateOfBirth = 1973-11-18 }
User { Id = 6, Name = Albert, City = Bratislava, DateOfBirth = 1940-12-11 }
User { Id = 8, Name = Robert, City = Bratislava, DateOfBirth = 1935-05-15 }
C# filter list with RemoveAll
The RemoveAll method removes all elements from a list that match
the conditions defined by a specified predicate. This method modifies the
original list in place.
List<int> numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
numbers.RemoveAll(n => n % 2 == 0);
Console.WriteLine(string.Join(",", numbers));
In this example, all even numbers are removed from the list. The
RemoveAll method takes a predicate and deletes all elements that
satisfy the condition.
$ dotnet run 1,3,5,7,9
Source
In this article we have learned how to filter a list in C# using various
techniques such as iteration, the FindAll method, the
RemoveAll method, LINQ query expressions, and the
Where method. Each method has its own advantages and use cases,
allowing developers to choose the most suitable approach for their specific
needs. Whether you prefer the simplicity of iteration, the convenience of
built-in methods, or the power of LINQ, C# provides flexible options for
efficiently filtering lists.
Author
List all C# tutorials.