Remove all null elements from a List in C#

This post will discuss how to remove all null elements from a list in C#.

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

List’s RemoveAll() method in-place removes all elements from a list that matches with the specified condition. It can be used as follows to remove null elements from a list of strings.

using System;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<string> strings = new List<string>() { "A", "B", null, "C", null };

strings.RemoveAll(s => s == null);

Console.WriteLine(String.Join(", ", strings)); // A, B, C

}

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The List<T>.RemoveAll() method accepts the Predicate<T> delegate that sets the conditions for the elements to be removed. To remove null, empty, and white-space characters from a list, you can use the predefined delegate IsNullOrWhiteSpace. Alternatively, you can use IsNullOrEmpty to remove null and empty strings from the List.

using System;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<string> strings = new List<string>() { "A", "B", null, "C", null };

strings.RemoveAll(string.IsNullOrEmpty);

Console.WriteLine(String.Join(", ", strings)); // A, B, C

}

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It is worth noting that the List<T>.Remove() method removes the first occurrence of the specified element from the list, and returns true if the item is successfully removed; false otherwise. Although not recommended, you can repeatedly invoke it within a loop to remove all occurrences of an element.

using System;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<string> strings = new List<string>() { "A", "B", null, "C", null };

while (strings.Remove(null)) {};

Console.WriteLine(String.Join(", ", strings)); // A, B, C

}

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2. Using `Enumerable.Where()` method

With LINQ, you can use the Enumerable.Where() method to filter a list on a predicate. Note that this creates a new list, but preserves the original ordering of the elements.

using System;

using System.Linq;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<string> strings = new List<string>() { "A", "B", null, "C", null };

strings = strings.Where(x => x != null).ToList();

Console.WriteLine(String.Join(", ", strings)); // A, B, C

}

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That’s all about removing all null elements from a list in C#.

Remove all null elements from a List in C#

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

2. Using Enumerable.Where() method

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

2. Using `Enumerable.Where()` method