How Can I Efficiently Remove Elements from C# Arrays?

Efficient method to remove array elements in C#

In C#, arrays are implemented as contiguous blocks of memory that store values ​​of the same type. However, unlike other collections such as ArrayLists, arrays have limited flexibility in element manipulation. Here's how to handle element deletion from an array:

Remove elements by value

To remove all instances of a specific value, you can use the .Where() LINQ extension method (if targeting .NET Framework 3.5 or later) or the .NET Framework 2.0's Array.FindAll() method. Consider the following code:

int[] numbers = { 1, 3, 4, 9, 2 };
int numToRemove = 4;

// LINQ
numbers = numbers.Where(val => val != numToRemove).ToArray();

// 非LINQ
numbers = Array.FindAll(numbers, isNotFour).ToArray();
bool isNotFour(int n) { return n != 4; }

Remove the first instance of the value

If you only want to remove the first instance of the value, you can again leverage the LINQ or non-LINQ approach:

int[] numbers = { 1, 3, 4, 9, 2, 4 };
int numToRemove = 4;

// LINQ
int numIdx = Array.IndexOf(numbers, numToRemove);
numbers = numbers.Where((val, idx) => idx != numIdx).ToArray();

// 非LINQ
int numIdx = Array.IndexOf(numbers, numToRemove);
List<int> tmp = new List<int>(numbers);
tmp.RemoveAt(numIdx);
numbers = tmp.ToArray();

In summary, while arrays provide efficient element storage and retrieval, they have limited flexibility in element manipulation, making methods such as RemoveAt() unsuitable. Instead, the method outlined above provides an efficient alternative for removing values ​​from an array.

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