Combine arrays

In C# two same-typed arrays can be merged. This task is often needed—for further processing in a program, we must combine arrays.

This allows us to use both parts of the data in a single collection. Several approaches are possible. They all have benefits and negatives.

AddRange

Here we use AddRange to combine arrays. This code is unlikely to fail due to off-by-one programming errors—it is reliable and clear.

using System;
using System.Collections.Generic;

// Part 1: declare 2 integer arrays.
int[] array1 = { 1, 2, 3, 4, 5 };
int[] array2 = { 6, 7, 8 };

// Part 2: create new List of integers and call AddRange twice.
var list = new List<int>();
list.AddRange(array1);
list.AddRange(array2);

// Part 3: call ToArray to convert List to array.
int[] array3 = list.ToArray();

// Part 4: loop through array elements of combined array and print them.
foreach (int element in array3)
{
    Console.WriteLine(element);
}
1
2
3
4
5
6
7
8

Array.Copy

This example program shows how to use Array.Copy to combine arrays. This is more efficient than the List approach. It only requires a new array.

using System;

int[] values1 = { 4, 4, 4 };
int[] values2 = { 5, 5 };

int[] all = new int[values1.Length + values2.Length];
Array.Copy(values1, all, values1.Length);
Array.Copy(values2, 0, all, values1.Length, values2.Length);

foreach (int value in all)
{
    Console.WriteLine(value);
}
4
4
4
5
5

BlockCopy

Next we use Buffer.BlockCopy to merge two int arrays. This method acts upon bytes, not elements (which are four bytes here).

using System;

// ... Two input arrays.
int[] array = { 1, 2, 3 };
int[] array2 = { 4, 5, 6 };

// ... Destination array.
int[] final = new int[array.Length + array2.Length];

// ... Copy first array.
Buffer.BlockCopy(array,
    0,
    final,
    0,
    array.Length * sizeof(int));

// ... Copy second.
//     Note the starting offset.
Buffer.BlockCopy(array2,
    0,
    final,
    array.Length * sizeof(int),
    array2.Length * sizeof(int));

// ... Display.
foreach (int value in final)
{
    Console.WriteLine(value);
}
1
2
3
4
5
6

AddRange, internals

Here we discuss the internal implementation of the AddRange() method. The AddRange method internally calls InsertRange.

Summary

With AddRange on the List we can combine arrays. This method will also work with more than 2 arrays. The arrays must all have the same type of elements.