How do I concatenate two arrays in C#?

Question

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 }));

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Right now I use

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

Is there an easier or more efficient method?

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Be careful with the Concat method. The post Array Concatenation in C# explains that:

var z = x.Concat(y).ToArray();

Will be inefficient for large arrays. That means the Concat method is only for meduim-sized arrays (up to 10000 elements).

Answer 1

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

Answer 2

Try this:

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

Answer 3

You could write an extension method:

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}