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C# filter list

last modified December 3, 2021

C# filter list tutorial shows how to filter a list in C#. C# tutorial is a comprehensive tutorial on C# language.

This tutorial shows several ways to filter a list in C# language. We use iteration, LINQ, and built-in FindAll method.

C# filter list with iteration

In the first example, we use a foreach loop to filter a list.

var words = new List { "sky", "rock", "forest", "new", "falcon", "jewelry" }; var filtered = new List[]; 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.

var words = new List { "sky", "rock", "forest", "new", "falcon", "jewelry" };

We have a list of words. The goal is to find out all words with three letters.

var filtered = new List[];

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.

var vals = new List {-1, -3, 0, 1, 3, 2, 9, -4}; List filtered = vals.FindAll[e => e > 0]; Console.WriteLine[string.Join[',', filtered]];

The example finds out all integer values that are greater than zero.

List 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.

var words = new List { "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.

C# filter list with LINQ Where

The next example filters a list with LINQ's Where method.

var vals = new List {-1, -3, 0, 1, 3, 2, 9, -4}; List filtered = vals.Where[x => x > 0].ToList[]; Console.WriteLine[string.Join[',', filtered]];

The example filters out all positive values.

List 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.

var cars = new List { 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 an array with Func

In the example, we use a Func delegate to filter an array of users.

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 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 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 }

In this tutorial, we have showed how to filter a list in C#.

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