Reputation: 196499

Remove element of a regular array

I have an array of Foo objects. How do I remove the second element of the array?

I need something similar to RemoveAt() but for a regular array.

Upvotes: 166

Answers (16)

James

Reputation: 2058

Um. Why is everyone allocating a new array?

Just copy the section after the 'removed' element down one index, and put null or default in final element.

Then you can get the benefits of a fixed length array (presumably important, if not using a list), while also not needing to iterate through every element checking for null (you break the loop on first null).

Upvotes: 0

Genci Ymeri

Reputation: 104

Try below code:

myArray = myArray.Where(s => (myArray.IndexOf(s) != indexValue)).ToArray();

myArray = myArray.Where(s => (s != "not_this")).ToArray();

Upvotes: 3

bonkmaykr

Reputation: 104

I know this article is ten years old and therefore probably dead, but here's what I'd try doing:

Use the IEnumerable.Skip() method, found in System.Linq. It will skip the selected element from the array, and return another copy of the array that only contains everything except the selected object. Then just repeat that for every element you want removed and after that save it to a variable.

For example, if we have an array named "Sample" (of type int[]) with 5 numbers. We want to remove the 2nd one, so trying "Sample.Skip(2);" should return the same array except without the 2nd number.

Upvotes: -2

user1618054

Reputation:

Here's a small collection of helper methods I produced based on some of the existing answers. It utilizes both extensions and static methods with reference parameters for maximum idealness:

public static class Arr
{
    public static int IndexOf<TElement>(this TElement[] Source, TElement Element)
    {
        for (var i = 0; i < Source.Length; i++)
        {
            if (Source[i].Equals(Element))
                return i;
        }

        return -1;
    }

    public static TElement[] Add<TElement>(ref TElement[] Source, params TElement[] Elements)
    {
        var OldLength = Source.Length;
        Array.Resize(ref Source, OldLength + Elements.Length);

        for (int j = 0, Count = Elements.Length; j < Count; j++)
            Source[OldLength + j] = Elements[j];

        return Source;
    }

    public static TElement[] New<TElement>(params TElement[] Elements)
    {
        return Elements ?? new TElement[0];
    }

    public static void Remove<TElement>(ref TElement[] Source, params TElement[] Elements)
    {
        foreach (var i in Elements)
            RemoveAt(ref Source, Source.IndexOf(i));
    }

    public static void RemoveAt<TElement>(ref TElement[] Source, int Index)
    {
        var Result = new TElement[Source.Length - 1];

        if (Index > 0)
            Array.Copy(Source, 0, Result, 0, Index);

        if (Index < Source.Length - 1)
            Array.Copy(Source, Index + 1, Result, Index, Source.Length - Index - 1);

        Source = Result;
    }
}

Performance wise, it is decent, but it could probably be improved. Remove relies on IndexOf and a new array is created for each element you wish to remove by calling RemoveAt.

IndexOf is the only extension method as it does not need to return the original array. New accepts multiple elements of some type to produce a new array of said type. All other methods must accept the original array as a reference so there is no need to assign the result afterward as that happens internally already.

I would've defined a Merge method for merging two arrays; however, that can already be accomplished with Add method by passing in an actual array versus multiple, individual elements. Therefore, Add may be used in the following two ways to join two sets of elements:

Arr.Add<string>(ref myArray, "A", "B", "C");

Arr.Add<string>(ref myArray, anotherArray);

Upvotes: 0

EdHellyer

Reputation: 721

I use this method for removing an element from an object array. In my situation, my arrays are small in length. So if you have large arrays you may need another solution.

private int[] RemoveIndices(int[] IndicesArray, int RemoveAt)
{
    int[] newIndicesArray = new int[IndicesArray.Length - 1];

    int i = 0;
    int j = 0;
    while (i < IndicesArray.Length)
    {
        if (i != RemoveAt)
        {
            newIndicesArray[j] = IndicesArray[i];
            j++;
        }

        i++;
    }

    return newIndicesArray;
}

Upvotes: 72

user2884232

Reputation: 25

    private int[] removeFromArray(int[] array, int id)
    {
        int difference = 0, currentValue=0;
        //get new Array length
        for (int i=0; i<array.Length; i++)
        {
            if (array[i]==id)
            {
                difference += 1;
            }
        }
        //create new array
        int[] newArray = new int[array.Length-difference];
        for (int i = 0; i < array.Length; i++ )
        {
            if (array[i] != id)
            {
                newArray[currentValue] = array[i];
                currentValue += 1;
            }
        }

        return newArray;
    }

Upvotes: 1

Jon Schneider

Reputation: 26973

LINQ one-line solution:

myArray = myArray.Where((source, index) => index != 1).ToArray();

The 1 in that example is the index of the element to remove -- in this example, per the original question, the 2nd element (with 1 being the second element in C# zero-based array indexing).

A more complete example:

string[] myArray = { "a", "b", "c", "d", "e" };
int indexToRemove = 1;
myArray = myArray.Where((source, index) => index != indexToRemove).ToArray();

After running that snippet, the value of myArray will be { "a", "c", "d", "e" }.

Upvotes: 60

Duncan

Reputation: 1550

As usual, I'm late to the party...

I'd like to add another option to the nice solutions list already present. =)
I would see this as a good opportunity for Extensions.

Reference: http://msdn.microsoft.com/en-us/library/bb311042.aspx

So, we define some static class and in it, our Method.
After that, we can use our extended method willy-nilly. =)

using System;

namespace FunctionTesting {

    // The class doesn't matter, as long as it's static
    public static class SomeRandomClassWhoseNameDoesntMatter {

        // Here's the actual method that extends arrays
        public static T[] RemoveAt<T>( this T[] oArray, int idx ) {
            T[] nArray = new T[oArray.Length - 1];
            for( int i = 0; i < nArray.Length; ++i ) {
                nArray[i] = ( i < idx ) ? oArray[i] : oArray[i + 1];
            }
            return nArray;
        }
    }

    // Sample usage...
    class Program {
        static void Main( string[] args ) {
            string[] myStrArray = { "Zero", "One", "Two", "Three" };
            Console.WriteLine( String.Join( " ", myStrArray ) );
            myStrArray = myStrArray.RemoveAt( 2 );
            Console.WriteLine( String.Join( " ", myStrArray ) );
            /* Output
             * "Zero One Two Three"
             * "Zero One Three"
             */

            int[] myIntArray = { 0, 1, 2, 3 };
            Console.WriteLine( String.Join( " ", myIntArray ) );
            myIntArray = myIntArray.RemoveAt( 2 );
            Console.WriteLine( String.Join( " ", myIntArray ) );
            /* Output
             * "0 1 2 3"
             * "0 1 3"
             */
        }
    }
}

Upvotes: 2

infografnet

Reputation: 4005

This is a way to delete an array element, as of .Net 3.5, without copying to another array - using the same array instance with Array.Resize<T>:

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: 12

Martin Brown

Reputation: 25310

Here is an old version I have that works on version 1.0 of the .NET framework and does not need generic types.

public static Array RemoveAt(Array source, int index)
{
    if (source == null)
        throw new ArgumentNullException("source");

    if (0 > index || index >= source.Length)
        throw new ArgumentOutOfRangeException("index", index, "index is outside the bounds of source array");

    Array dest = Array.CreateInstance(source.GetType().GetElementType(), source.Length - 1);
    Array.Copy(source, 0, dest, 0, index);
    Array.Copy(source, index + 1, dest, index, source.Length - index - 1);

    return dest;
}

This is used like this:

class Program
{
    static void Main(string[] args)
    {
        string[] x = new string[20];
        for (int i = 0; i < x.Length; i++)
            x[i] = (i+1).ToString();

        string[] y = (string[])MyArrayFunctions.RemoveAt(x, 3);

        for (int i = 0; i < y.Length; i++)
            Console.WriteLine(y[i]);
    }
}

Upvotes: 6

Bamara Coulibaly

Reputation: 737

First step
You need to convert the array into a list, you could write an extension method like this

// Convert An array of string  to a list of string
public static List<string> ConnvertArrayToList(this string [] array) {

    // DECLARE a list of string and add all element of the array into it

    List<string> myList = new List<string>();
    foreach( string s in array){
        myList.Add(s);
    }
    return myList;
}

Second step
Write an extension method to convert back the list into an array

// convert a list of string to an array 
public static string[] ConvertListToArray(this List<string> list) {

    string[] array = new string[list.Capacity];
    array = list.Select(i => i.ToString()).ToArray();
    return array;
}

Last steps
Write your final method, but remember to remove the element at index before converting back to an array like the code show

public static string[] removeAt(string[] array, int index) {

    List<string> myList = array.ConnvertArrayToList();
    myList.RemoveAt(index);
    return myList.ConvertListToArray();
}

examples codes could be find on my blog, keep tracking.

Upvotes: -5

nawfal

Reputation: 73183

Not exactly the way to go about this, but if the situation is trivial and you value your time, you can try this for nullable types.

Foos[index] = null

and later check for null entries in your logic..

Upvotes: 5

Andrew Kennan

Reputation: 14157

If you don't want to use List:

var foos = new List<Foo>(array);
foos.RemoveAt(index);
return foos.ToArray();

You could try this extension method that I haven't actually tested:

public static T[] RemoveAt<T>(this T[] source, int index)
{
    T[] dest = new T[source.Length - 1];
    if( index > 0 )
        Array.Copy(source, 0, dest, 0, index);

    if( index < source.Length - 1 )
        Array.Copy(source, index + 1, dest, index, source.Length - index - 1);

    return dest;
}

And use it like:

Foo[] bar = GetFoos();
bar = bar.RemoveAt(2);

Upvotes: 242

Sebastian Dietz

Reputation: 5706

The nature of arrays is that their length is immutable. You can't add or delete any of the array items.

You will have to create a new array that is one element shorter and copy the old items to the new array, excluding the element you want to delete.

So it is probably better to use a List instead of an array.

Upvotes: 85

gkrogers

Reputation: 8356

In a normal array you have to shuffle down all the array entries above 2 and then resize it using the Resize method. You might be better off using an ArrayList.

Upvotes: 1

Paul Mitchell

Reputation: 3281

Here's how I did it...

    public static ElementDefinitionImpl[] RemoveElementDefAt(
        ElementDefinition[] oldList,
        int removeIndex
    )
    {
        ElementDefinitionImpl[] newElementDefList = new ElementDefinitionImpl[ oldList.Length - 1 ];

        int offset = 0;
        for ( int index = 0; index < oldList.Length; index++ )
        {
            ElementDefinitionImpl elementDef = oldList[ index ] as ElementDefinitionImpl;
            if ( index == removeIndex )
            {
                //  This is the one we want to remove, so we won't copy it.  But 
                //  every subsequent elementDef will by shifted down by one.
                offset = -1;
            }
            else
            {
                newElementDefList[ index + offset ] = elementDef;
            }
        }
        return newElementDefList;
    }

Upvotes: 1

Remove element of a regular array

Answers (16)

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