Conditionally remove items from a list in C#

This post will discuss how to conditionally remove items from a list in C#.

1. Using `List<T>.RemoveAll()` Method

To remove elements from a list that satisfies a given predicate in C#, you can use the List<T>.RemoveAll() method. The following code example shows a typical invocation for this method. Note that this uses LINQ.

using System;

using System.Linq;

using System.Collections.Generic;

public class Company

{

public string name;

public int founded;

public Company(string name, int founded)

{

this.name = name;

this.founded = founded;

}

public override string ToString() {

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

}

public class Example

{

public static void Main()

{

List<Company> cars = new List<Company>();

cars.Add(new Company("Ford", 1903));

cars.Add(new Company("Chevrolet", 1908));

cars.Add(new Company("Toyota", 1937));

cars.Add(new Company("Honda", 1948));

cars.RemoveAll(s => s.founded > 1920);

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

}

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Output:

[Ford, 1903], [Chevrolet, 1908]

2. Using `Remove()` Method

In order to remove a single occurrence of an element from a list that satisfies a given predicate in C#, you can use the List<T>.Remove() method from LINQ. This method is demonstrated below using the Single() method that returns the only element of a sequence that satisfies a specified condition.

using System;

using System.Linq;

using System.Collections.Generic;

public class Company

{

public string name;

public int founded;

public Company(string name, int founded)

{

this.name = name;

this.founded = founded;

}

public override string ToString() {

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

}

public class Example

{

public static void Main()

{

List<Company> cars = new List<Company>();

cars.Add(new Company("Ford", 1903));

cars.Add(new Company("Chevrolet", 1908));

cars.Add(new Company("Toyota", 1937));

cars.Add(new Company("Honda", 1948));

cars.Remove(cars.Single(s => s.founded == 1948));

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

}

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Output:

[Ford, 1903], [Chevrolet, 1908], [Toyota, 1937]

The List<T>.Remove() method throws System.InvalidOperationException if the sequence contains no matching element. This can be handled using the SingleOrDefault() method that returns a default value if the matching element is not found.

using System;

using System.Linq;

using System.Collections.Generic;

public class Company

{

public string name;

public int founded;

public Company(string name, int founded)

{

this.name = name;

this.founded = founded;

}

public override string ToString() {

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

}

public class Example

{

public static void Main()

{

List<Company> cars = new List<Company>();

cars.Add(new Company("Ford", 1903));

cars.Add(new Company("Chevrolet", 1908));

cars.Add(new Company("Toyota", 1937));

cars.Add(new Company("Honda", 1948));

var toRemove = cars.SingleOrDefault(s => s.founded == 1948);

if (toRemove != null) {

cars.Remove(toRemove);

}

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

}

Download Run Code

Output:

[Ford, 1903], [Chevrolet, 1908], [Toyota, 1937]

Note that both Single() and SingleOrDefault() method throws System.InvalidOperationException if the sequence contains more than one matching element. Finally, in order to remove all occurrences of matching elements from a list, you can invoke the List<T>.Remove() method for each matching element. Here’s an example of its usage:

using System;

using System.Linq;

using System.Collections.Generic;

public class Company

{

public string name;

public int founded;

public Company(string name, int founded)

{

this.name = name;

this.founded = founded;

}

public override string ToString() {

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

}

public class Example

{

public static void Main()

{

List<Company> cars = new List<Company>();

cars.Add(new Company("Ford", 1903));

cars.Add(new Company("Chevrolet", 1948));

cars.Add(new Company("Toyota", 1937));

cars.Add(new Company("Honda", 1948));

var toRemove = cars.Where(item => item.founded == 1948).ToList();

foreach (var s in toRemove) {

cars.Remove(s);

}

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

}

Download Run Code

Output:

[Ford, 1903], [Toyota, 1937]

That’s all about conditionally removing items from a list in C#.

Conditionally remove items from a list in C#

1. Using List<T>.RemoveAll() Method

2. Using Remove() Method

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1. Using `List<T>.RemoveAll()` Method

2. Using `Remove()` Method