In C#, how can I concatenate two arrays?

Problem

int[] x = new int [] { 1, 2, 3};
int[] y = new int [] { 4, 5 };

int[] z = // your answer here...

Debug.Assert(z.SequenceEqual(new int[] { 1, 2, 3, 4, 5 }));

I’m currently using

int[] z = x.Concat(y).ToArray();

Is there a better or more efficient way to do this?

Asked by hwiechers

Solution #1

var z = new int[x.Length + y.Length];
x.CopyTo(z, 0);
y.CopyTo(z, x.Length);

Answered by Zed

Solution #2

Try this:

List<int> list = new List<int>();
list.AddRange(x);
list.AddRange(y);
int[] z = list.ToArray();

Answered by Adriaan Stander

Solution #3

You might make an extension method like this:

public static T[] Concat<T>(this T[] x, T[] y)
{
    if (x == null) throw new ArgumentNullException("x");
    if (y == null) throw new ArgumentNullException("y");
    int oldLen = x.Length;
    Array.Resize<T>(ref x, x.Length + y.Length);
    Array.Copy(y, 0, x, oldLen, y.Length);
    return x;
}

Then:

int[] x = {1,2,3}, y = {4,5};
int[] z = x.Concat(y); // {1,2,3,4,5}

Answered by Marc Gravell

Solution #4

I came up with a more general-purpose method that allows you to concatenate any number of one-dimensional arrays of the same type. (I was concatenating three or more items at a time.)

My function:

    public static T[] ConcatArrays<T>(params T[][] list)
    {
        var result = new T[list.Sum(a => a.Length)];
        int offset = 0;
        for (int x = 0; x < list.Length; x++)
        {
            list[x].CopyTo(result, offset);
            offset += list[x].Length;
        }
        return result;
    }

And usage:

        int[] a = new int[] { 1, 2, 3 };
        int[] b = new int[] { 4, 5, 6 };
        int[] c = new int[] { 7, 8 };
        var y = ConcatArrays(a, b, c); //Results in int[] {1,2,3,4,5,6,7,8}

Answered by deepee1

Solution #5

This is it:

using System.Linq;

int[] array1 = { 1, 3, 5 };
int[] array2 = { 0, 2, 4 };

// Concatenate array1 and array2.
var result1 = array1.Concat(array2);

Answered by Roland

Post is based on https://stackoverflow.com/questions/1547252/how-do-i-concatenate-two-arrays-in-c