Filter a List in C#

This post will discuss how to filter a list in C#.

1. Using `Enumerable.Where()` Method

A simple and elegant solution to filter a list is using LINQ. It has a Where() method that filters a sequence of values based on the specified predicate. The following code example demonstrates how we can use Where() for filtering a list.

using System;

using System.Linq;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<int> list = new List<int> { 1, 2, 3, 4, 5, 6, 7 };

List<int> odd = list.Where(x => x % 2 == 1).ToList();

Console.WriteLine(String.Join(", ", odd)); // 1, 3, 5, 7

}

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Note that the above solution allocates a new list. The following code example uses the Where() clause to filter a sequence of objects by their age.

using System;

using System.Linq;

using System.Collections.Generic;

public class Person

{

public string name { get; set; }

public int age { get; set; }

public Person(string name, int age)

{

this.name = name;

this.age = age;

}

public override string ToString() {

return "[" + name + ", " + age + "]";

}

public class Example

{

public static void Main()

{

List<Person> list = new List<Person> {

new Person("x", 27), new Person("y", 20),

new Person("z", 24), new Person("z", 30)

};

List<Person> filteredList = list.Where(item => item.age > 25).ToList();

Console.WriteLine(String.Join(", ", filteredList));

}

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2. Using `List<T>.FindAll()` Method

The List<T>.FindAll() method retrieves all elements of the list that matches with the specified predicate delegate. We can use it as follows to filter a list in C#.

using System;

using System.Linq;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<int> list = new List<int> { 1, 2, 3, 4, 5, 6, 7 };

List<int> odd = list.FindAll(x => x % 2 == 1).ToList();

Console.WriteLine(String.Join(", ", odd)); // 1, 3, 5, 7

}

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That’s all about filtering a list in C#.

1. Using Enumerable.Where() Method

2. Using List<T>.FindAll() Method

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1. Using `Enumerable.Where()` Method

2. Using `List<T>.FindAll()` Method