CODEWITHSUNDEEP
c#.netarrays
ahmed
ahmed

Reputation: 14666

How to delete an element from an array in C#

Lets say I have this array,

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

How can I delete an element by "name"? , lets say number 4?

Even ArrayList didn't help to delete?

string strNumbers = " 1, 3, 4, 9, 2";
ArrayList numbers = new ArrayList(strNumbers.Split(new char[] { ',' }));
numbers.RemoveAt(numbers.IndexOf(4));
foreach (var n in numbers)
{
    Response.Write(n);
}

Upvotes: 215

Views: 782167

Answers (13)

David Eckardt
David Eckardt

Reputation: 89

In recent C#/.NET featuring the Span<T> type and range expressions this can be done using the Span.CopyTo method to move array elements around:

// Removes a[i..i+n], fast but not preserving the order of array elements.
void arrayRemoveAtFast<T>(ref T[] a, int i, int n)
{
    // Create a Span that references the array elements.
    var s = a.AsSpan();
    // Copy the last n array elements to positions i…i+n.
    // Caveat: Use `s`, not `a`, or else the result may be invalid.
    s[^n..].CopyTo(s[i..(i+n)]);
    // Cut the last n array elements off.
    a = a[..^n];
}

// Removes a[i..i+n], preserving the order of array elements.
void arrayRemoveAtPreserveOrder<T>(ref T[] a, int i, int n)
{
    // Create a Span that references the array elements.
    var s = a.AsSpan();
    // Move array elements that follow the ones to remove to the front.
    // Caveat: Use `s`, not `a`, or else the result may be invalid.
    s[(i + n)..].CopyTo(s[i..^n]);
    // Cut the last n array elements off.
    a = a[..^n];
}

Upvotes: 1

arman aramesh
arman aramesh

Reputation: 7

We can delete array elements by using for loops and continue statements:

string[] cars = {"volvo", "benz", "ford", "bmw"};
for (int i = 0; i < cars.Length; i++)
{
    if (cars[i] == "benz")
    {
        continue;
    }
    Console.WriteLine(cars[i]);
}

Upvotes: -6

Varun Kumar
Varun Kumar

Reputation: 7

    public int[] DeletePart(int position, params int[] numbers)
    {
        int[] result = new int[numbers.Length - 1];
        int z=0;

        for (int i = 0; i < numbers.Length; i++)
        {
            if (position - 1 != i)
            {
                result[z] = numbers[i];
                z++;
            }
        }
        return result;
    }

Upvotes: 0

user4860969
user4860969

Reputation:

You can do in this way:

int[] numbers= {1,3,4,9,2};     
List<int> lst_numbers = new List<int>(numbers);
int required_number = 4;
int i = 0;
foreach (int number in lst_numbers)
{              
    if(number == required_number)
    {
        break;
    }
    i++;
}
lst_numbers.RemoveAt(i);
numbers = lst_numbers.ToArray();

Upvotes: 2

ctacke
ctacke

Reputation: 67178

Removing from an array itself is not simple, as you then have to deal with resizing. This is one of the great advantages of using something like a List<int> instead. It provides Remove/RemoveAt in 2.0, and lots of LINQ extensions for 3.0.

If you can, refactor to use a List<> or similar.

Upvotes: 7

infografnet
infografnet

Reputation: 4005

I posted my solution here.

This is a way to delete an array element without copying to another array - just in frame of the same array instance:

    public static void RemoveAt<T>(ref T[] arr, int index)
    {
        for (int a = index; a < arr.Length - 1; a++)
        {
            // moving elements downwards, to fill the gap at [index]
            arr[a] = arr[a + 1];
        }
        // finally, let's decrement Array's size by one
        Array.Resize(ref arr, arr.Length - 1);
    }

Upvotes: 10

Petrucio
Petrucio

Reputation: 5679

As a generic extension, 2.0-compatible:

using System.Collections.Generic;
public static class Extensions {
    //=========================================================================
    // Removes all instances of [itemToRemove] from array [original]
    // Returns the new array, without modifying [original] directly
    // .Net2.0-compatible
    public static T[] RemoveFromArray<T> (this T[] original, T itemToRemove) {  
        int numIdx = System.Array.IndexOf(original, itemToRemove);
        if (numIdx == -1) return original;
        List<T> tmp = new List<T>(original);
        tmp.RemoveAt(numIdx);
        return tmp.ToArray();
    }
}

Usage:

int[] numbers = {1, 3, 4, 9, 2};
numbers = numbers.RemoveFromArray(4);

Upvotes: 5

SP007
SP007

Reputation: 1921

' To remove items from string based on Dictionary key values. ' VB.net code

 Dim stringArr As String() = "file1,file2,file3,file4,file5,file6".Split(","c)
 Dim test As Dictionary(Of String, String) = New Dictionary(Of String, String)
 test.Add("file3", "description")
 test.Add("file5", "description")
 stringArr = stringArr.Except(test.Keys).ToArray()

Upvotes: 1

BenAlabaster
BenAlabaster

Reputation: 39816

If you want to remove all instances of 4 without needing to know the index:

LINQ: (.NET Framework 3.5)

int[] numbers = { 1, 3, 4, 9, 2 };
int numToRemove = 4;
numbers = numbers.Where(val => val != numToRemove).ToArray();

Non-LINQ: (.NET Framework 2.0)

static bool isNotFour(int n)
{
    return n != 4;
}

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

If you want to remove just the first instance:

LINQ: (.NET Framework 3.5)

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();

Non-LINQ: (.NET Framework 2.0)

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();

Edit: Just in case you hadn't already figured it out, as Malfist pointed out, you need to be targetting the .NET Framework 3.5 in order for the LINQ code examples to work. If you're targetting 2.0 you need to reference the Non-LINQ examples.

Upvotes: 441

Dave DP
Dave DP

Reputation: 541

You can also convert your array to a list and call remove on the list. You can then convert back to your array.

int[] numbers = {1, 3, 4, 9, 2};
var numbersList = numbers.ToList();
numbersList.Remove(4);

Upvotes: 35

meetjaydeep
meetjaydeep

Reputation: 1850

int[] numbers = { 1, 3, 4, 9, 2 };
numbers = numbers.Except(new int[]{4}).ToArray();

Upvotes: 46

DevinB
DevinB

Reputation: 8316

The code that is written in the question has a bug in it

Your arraylist contains strings of " 1" " 3" " 4" " 9" and " 2" (note the spaces)

So IndexOf(4) will find nothing because 4 is an int, and even "tostring" would convert it to of "4" and not " 4", and nothing will get removed.

An arraylist is the correct way to go to do what you want.

Upvotes: 12

Vojislav Stojkovic
Vojislav Stojkovic

Reputation: 8153

Balabaster's answer is correct if you want to remove all instances of the element. If you want to remove only the first one, you would do something like this:

int[] numbers = { 1, 3, 4, 9, 2, 4 };
int numToRemove = 4;
int firstFoundIndex = Array.IndexOf(numbers, numToRemove);
if (numbers >= 0)
{
    numbers = numbers.Take(firstFoundIndex).Concat(numbers.Skip(firstFoundIndex + 1)).ToArray();
}

Upvotes: 6

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