How to Efficiently Delete Elements from a C# Array by Value?

Remove elements from array in C#

Scene:

Suppose you have an array of integers:

<code class="language-c#">int[] numbers = {1, 3, 4, 9, 2};</code>

You want to remove elements with a specific value (for example, 4). Although you can use ArrayList to manage arrays, its RemoveAt method does not allow filtering based on element values.

Solution:

To remove elements from an array by name (value), you can use LINQ or non-LINQ methods.

LINQ method (.NET Framework 3.5):

Using LINQ’s Where method, you can filter elements and exclude those you want to delete:

<code class="language-c#">int[] numbers = { 1, 3, 4, 9, 2 };
int numToRemove = 4;
numbers = numbers.Where(val => val != numToRemove).ToArray();</code>

Non-LINQ method (.NET Framework 2.0):

For environments without LINQ, you can use the built-in Array method to achieve the same result:

<code class="language-c#">static bool isNotFour(int n)
{
    return n != 4;
}

int[] numbers = { 1, 3, 4, 9, 2 };
numbers = Array.FindAll(numbers, isNotFour);</code>

Delete only the first instance:

If you only want to remove the first occurrence of a specific element:

LINQ method:

<code class="language-c#">int[] numbers = { 1, 3, 4, 9, 2, 4 };
int numToRemove = 4;
int numIndex = Array.IndexOf(numbers, numToRemove);
numbers = numbers.Where((val, idx) => idx != numIndex).ToArray();</code>

Non-LINQ methods:

<code class="language-c#">int[] numbers = { 1, 3, 4, 9, 2, 4 };
int numToRemove = 4;
int numIdx = Array.IndexOf(numbers, numToRemove);
List<int> tmp = new List<int>(numbers);
tmp.RemoveAt(numIdx);
numbers = tmp.ToArray();</code>

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