Reputation: 3444

Merging two arrays in .NET

Is there a built in function in .NET 2.0 that will take two arrays and merge them into one array?

The arrays are both of the same type. I'm getting these arrays from a widely used function within my code base and can't modify the function to return the data in a different format.

I'm looking to avoid writing my own function to accomplish this if possible.

Upvotes: 310

Answers (28)

Mondonno

Reputation: 181

There is another way to do this, that does not require any additional references to internal libraries (except of course System.Collections.Generic)

public static IEnumerable<T> Merge<T>(IEnumerable<T> first, 
                                           IEnumerable<T> second)
{
    foreach(var e in first)
        yield return e;
    foreach(var e in second)
        yield return e;
}

This solution is more universal because of the fact that it uses IEnumerable<T>, it means that it can merge elements from any two iterators, and returns a third iterator which contains elements from first and second one.

Here is snippet of example usage.

Upvotes: -1

marsze

Reputation: 17035

Since .NET 5, we now have AllocateUninitializedArray, which can add an additional small performance improvement for larger arrays:

public static T[] ConcatArrays<T>(IEnumerable<T[]> arrays)
{
    var result = GC.AllocateUninitializedArray<T>(arrays.Sum(a => a.Length));
    var offset = 0;
    foreach (var a in arrays)
    {
        a.CopyTo(result, offset);
        offset += a.Length;
    }
    return result;
}

Upvotes: 1

Oleksandr Pyrohov

Reputation: 16216

Starting from C# 12 you may use the Collection Expressions and spread operator .., for example:

int[] a = [1, 2, 3];
int[] b = [4, 5, 6];
int[] c = [..a, ..b];

Note: The feature is part of .NET 8 released in Nov 2023.

Upvotes: 27

cskwg

Reputation: 849

For an efficient solution, you might try this one:

        //
    ///<summary>Join two arrays together. At least one array must exist.</summary>
    public static T[] Append<T>( this T[] a1, T[] a2 ) {
        if ( null == a1 && null == a2 ) return null;
        int l1 = 0;
        if ( null != a1 ) l1 = a1.Length;
        int l2 = 0;
        if ( null != a2 ) l2 = a2.Length;
        var b = new T[ l1 + l2 ];
        if ( null != a1 ) Array.Copy( a1, b, l1 );
        if ( null != a2 ) Array.Copy( a2, 0, b, l1, l2 );
        return b;
    }

Upvotes: 0

ArrayFormula

Reputation: 1

I wanted to find an approach without using any libraries or functionality beyond arrays themselves.

The first two examples are mostly for reading the logic from scratch, but I also wonder if there could be performance variations depending on the sitaution.

The third example is the most practical choice.

// Two for-loops
private static int[] MergedArrays_1(int[] a, int[] b)
{
    int[] result = new int[a.Length + b.Length];
    for (int i = 0; i < a.Length; i++)
    {
        result[i] = a[i];
    }
    for (int i = a.Length; i < result.Length; i++)
    {
        result[i] = b[i - a.Length];
    }
    return result;
}

// One for-loop
private static int[] MergedArrays_2(int[] a, int[] b)
{
    int[] results = new int[a.Length + b.Length];
    for (int i = 0; i < results.Length; i++)
    {
        results[i] = (i < a.Length) ? a[i] : b[i - a.Length];
    }
    return results;
}

// Array Method
private static int[] MergedArrays_3(int[] a, int[] b)
{
    int[] results = new int[a.Length + b.Length];
    a.CopyTo(results, 0);
    b.CopyTo(results, a.Length);
    return results;
}

Lastly, I made a fourth example, that can merge multiple arrays, using the params keyword.

int[] result = MultipleMergedArrays(arrayOne, arrayTwo, arrayThree);

private static int[] MultipleMergedArrays(params int[][] a)
{
    // Get Length
    int resultsLength = 0;
    for (int row = 0; row < a.GetLength(0); row++)
    {
        resultsLength += a.Length;
    }

    // Initialize
    int[] results = new int[resultsLength];

    // Add Items
    int index = 0;
    for (int row = 0; row < a.GetLength(0); row++)
    {
        a[row].CopyTo(results, index);
        index += a[row].Length;
    }
    return results;
}

The way it works when using params, is that the single-dimension arrays are passed into a jagged array.

GetLength(0) returns the number of arrays contained within the jagged array.

The code first counts the Length of all the arrays, then it initializes a new array based on that size, and starts adding entire arrays into the new results array by using the CopyTo() method, while adding the Length of each added array to an index counter.

PS: Some times it is necessary to remove empty items, or certain items, from arrays when merging.

private static int[] RemoveEmpty(int[] array)
{
    int count = 0;
    for (int i = 0; i < array.Length; i++)
    {
        if (array[i] == 0) count++;
    }

    int[] result = new int[array.Length - count];

    count = 0;
    for (int i = 0; i < array.Length; i++)
    {
        if (array[i] == 0) continue;
        result[count] = array[i];
        count++;
    }

    return result;
}

This function can be combined with the ones above.

It takes an array, counts the number of items that match zero. And creates a new array of the proper size. Then the counter is recycled and used as an index, for where to put place the input array's values into the new and smaller result array. When an item matches zero, it skips the rest of the code in that round of the loop, and continues with the next round, without incrementing the integer counter.

Upvotes: 0

Harjeet Singh

Reputation: 11

string[] names1 = new string[] { "Ava", "Emma", "Olivia" };
string[] names2 = new string[] { "Olivia", "Sophia", "Emma" };
List<string> arr = new List<string>(names1.Length + names2.Length);
arr.AddRange(names1);
arr.AddRange(names2);
string[] result = arr.Distinct().ToArray();
foreach(string str in result)
{
    Console.WriteLine(str.ToString());
}

Console.ReadLine();

Upvotes: 1

Dmitry Shashurov

Reputation: 1694

Simple code to join multiple arrays:

string[] arr1 = ...
string[] arr2 = ...
string[] arr3 = ...    
List<string> arr = new List<string>(arr1.Length + arr2.Length + arr3.Length);
arr.AddRange(arr1);
arr.AddRange(arr2);
arr.AddRange(arr3);
string[] result = arr.ToArray();

Upvotes: -1

schoetbi

Reputation: 12846

If you have the source arrays in an array itself you can use SelectMany:

var arrays = new[]{new[]{1, 2, 3}, new[]{4, 5, 6}};
var combined = arrays.SelectMany(a => a).ToArray();
foreach (var v in combined) Console.WriteLine(v);

gives

Probably this is not the fastest method but might fit depending on usecase.

Upvotes: 4

Simon B.

Reputation: 1685

Use LINQ:

var arr1 = new[] { 1, 2, 3, 4, 5 };
var arr2 = new[] { 6, 7, 8, 9, 0 };
var arr = arr1.Union(arr2).ToArray();

Keep in mind, this will remove duplicates. If you want to keep duplicates, use Concat.

Upvotes: 158

cj.burrow

Reputation: 333

This is what I came up with. Works for a variable number of arrays.

public static T[] ConcatArrays<T>(params T[][] args)
    {
        if (args == null)
            throw new ArgumentNullException();

        var offset = 0;
        var newLength = args.Sum(arr => arr.Length); 
        var newArray = new T[newLength];

        foreach (var arr in args)
        {
            Buffer.BlockCopy(arr, 0, newArray, offset, arr.Length);
            offset += arr.Length;
        }

        return newArray;
    }

...

var header = new byte[] { 0, 1, 2};
var data = new byte[] { 3, 4, 5, 6 };
var checksum = new byte[] {7, 0};
var newArray = ConcatArrays(header, data, checksum);
//output byte[9] { 0, 1, 2, 3, 4, 5, 6, 7, 0 }

Upvotes: 8

Simon_Weaver

Reputation: 145880

I needed a solution to combine an unknown number of arrays.

Surprised nobody else provided a solution using SelectMany with params.

 private static T[] Combine<T>(params IEnumerable<T>[] items) =>
                    items.SelectMany(i => i).Distinct().ToArray();

If you don't want distinct items just remove distinct.

 public string[] Reds = new [] { "Red", "Crimson", "TrafficLightRed" };
 public string[] Greens = new [] { "Green", "LimeGreen" };
 public string[] Blues = new [] { "Blue", "SkyBlue", "Navy" };

 public string[] Colors = Combine(Reds, Greens, Blues);

Note: There is definitely no guarantee of ordering when using distinct.

Upvotes: 3

Joel Coehoorn

Reputation: 415600

Assuming the destination array has enough space, Array.Copy() will work. You might also try using a List<T> and its .AddRange() method.

Upvotes: 5

Lord Darth Vader

Reputation: 2005

Created and extension method to handle null

public static class IEnumerableExtenions
{
    public static IEnumerable<T> UnionIfNotNull<T>(this IEnumerable<T> list1, IEnumerable<T> list2)
    {
        if (list1 != null && list2 != null)
            return list1.Union(list2);
        else if (list1 != null)
            return list1;
        else if (list2 != null)
            return list2;
        else return null;
    }
}

Upvotes: 0

Smith

Reputation: 5951

If you don't want to remove duplicates, then try this

Use LINQ:

var arr1 = new[] { 1, 2, 3, 4, 5 };
var arr2 = new[] { 6, 7, 8, 9, 0 };
var arr = arr1.Concat(arr2).ToArray();

Upvotes: 59

Solomon Rutzky

Reputation: 48776

Just to have it noted as an option: if the arrays you are working with are of a primitive type – Boolean (bool), Char, SByte, Byte, Int16 (short), UInt16, Int32 (int), UInt32, Int64 (long), UInt64, IntPtr, UIntPtr, Single, or Double – then you could (or should?) try using Buffer.BlockCopy. According to the MSDN page for the Buffer class:

This class provides better performance for manipulating primitive types than similar methods in the System.Array class.

Using the C# 2.0 example from @OwenP's answer as a starting point, it would work as follows:

int[] front = { 1, 2, 3, 4 };
int[] back = { 5, 6, 7, 8 };

int[] combined = new int[front.Length + back.Length];
Buffer.BlockCopy(front, 0, combined, 0, front.Length);
Buffer.BlockCopy(back, 0, combined, front.Length, back.Length);

There is barely any difference in syntax between Buffer.BlockCopy and the Array.Copy that @OwenP used, but this should be faster (even if only slightly).

Upvotes: 4

John Reilly

Reputation: 6259

Everyone has already had their say but I think this more readable than the "use as Extension method" approach:

var arr1 = new[] { 1, 2, 3, 4, 5 };
var arr2 = new[] { 6, 7, 8, 9, 0 };
var arr = Queryable.Concat(arr1, arr2).ToArray();

However it can only be used when bringing together 2 arrays.

Upvotes: 5

Blair Conrad

Reputation: 241714

If you can manipulate one of the arrays, you can resize it before performing the copy:

T[] array1 = getOneArray();
T[] array2 = getAnotherArray();
int array1OriginalLength = array1.Length;
Array.Resize<T>(ref array1, array1OriginalLength + array2.Length);
Array.Copy(array2, 0, array1, array1OriginalLength, array2.Length);

Otherwise, you can make a new array

T[] array1 = getOneArray();
T[] array2 = getAnotherArray();
T[] newArray = new T[array1.Length + array2.Length];
Array.Copy(array1, newArray, array1.Length);
Array.Copy(array2, 0, newArray, array1.Length, array2.Length);

More on available Array methods on MSDN.

Upvotes: 142

Angelo Ortega

Reputation: 461

Easier would just be using LINQ:

var array = new string[] { "test" }.ToList();
var array1 = new string[] { "test" }.ToList();
array.AddRange(array1);
var result = array.ToArray();

First convert the arrays to lists and merge them... After that just convert the list back to an array :)

Upvotes: 11

namco

Reputation: 6338

Try this:

ArrayLIst al = new ArrayList();
al.AddRange(array_1);
al.AddRange(array_2);
al.AddRange(array_3);
array_4 = al.ToArray();

Upvotes: -2

OwenP

Reputation: 25378

In C# 3.0 you can use LINQ's Concat method to accomplish this easily:

int[] front = { 1, 2, 3, 4 };
int[] back = { 5, 6, 7, 8 };
int[] combined = front.Concat(back).ToArray();

In C# 2.0 you don't have such a direct way, but Array.Copy is probably the best solution:

int[] front = { 1, 2, 3, 4 };
int[] back = { 5, 6, 7, 8 };

int[] combined = new int[front.Length + back.Length];
Array.Copy(front, combined, front.Length);
Array.Copy(back, 0, combined, front.Length, back.Length);

This could easily be used to implement your own version of Concat.

Upvotes: 565

Rajkumar M

Reputation: 11

This code will work for all cases:

int[] a1 ={3,4,5,6};
int[] a2 = {4,7,9};
int i = a1.Length-1;
int j = a2.Length-1;
int resultIndex=  i+j+1;
Array.Resize(ref a2, a1.Length +a2.Length);
while(resultIndex >=0)
{
    if(i != 0 && j !=0)
    {
        if(a1[i] > a2[j])
        {
            a2[resultIndex--] = a[i--];
        }
        else
        {
            a2[resultIndex--] = a[j--];
        }
    }
    else if(i>=0 && j<=0)
    { 
        a2[resultIndex--] = a[i--];
    }
    else if(j>=0 && i <=0)
    {
       a2[resultIndex--] = a[j--];
    }
}

Upvotes: -1

Lukas

Reputation: 2923

In case someone else is looking for how to merge two image byte arrays:

        private void LoadImage()
        {
            string src = string.empty;
            byte[] mergedImageData = new byte[0];

            mergedImageData = MergeTwoImageByteArrays(watermarkByteArray, backgroundImageByteArray);
            src = "data:image/png;base64," + Convert.ToBase64String(mergedImageData);
            MyImage.ImageUrl = src;
        }

        private byte[] MergeTwoImageByteArrays(byte[] imageBytes, byte[] imageBaseBytes)
        {
            byte[] mergedImageData = new byte[0];
            using (var msBase = new MemoryStream(imageBaseBytes))
            {
                System.Drawing.Image imgBase = System.Drawing.Image.FromStream(msBase);
                Graphics gBase = Graphics.FromImage(imgBase);
                using (var msInfo = new MemoryStream(imageBytes))
                {
                    System.Drawing.Image imgInfo = System.Drawing.Image.FromStream(msInfo);
                    Graphics gInfo = Graphics.FromImage(imgInfo);
                    gBase.DrawImage(imgInfo, new Point(0, 0));
                    //imgBase.Save(Server.MapPath("_____testImg.png"), ImageFormat.Png);
                    MemoryStream mergedImageStream = new MemoryStream();
                    imgBase.Save(mergedImageStream, ImageFormat.Png);
                    mergedImageData = mergedImageStream.ToArray();
                    mergedImageStream.Close();
                }
            }
            return mergedImageData;
        }

Upvotes: 1

Lorenz Lo Sauer

Reputation: 24690

Personally, I prefer my own Language Extensions, which I add or remove at will for rapid prototyping.

Following is an example for strings.

//resides in IEnumerableStringExtensions.cs
public static class IEnumerableStringExtensions
{
   public static IEnumerable<string> Append(this string[] arrayInitial, string[] arrayToAppend)
   {
       string[] ret = new string[arrayInitial.Length + arrayToAppend.Length];
       arrayInitial.CopyTo(ret, 0);
       arrayToAppend.CopyTo(ret, arrayInitial.Length);

       return ret;
   }
}

It is much faster than LINQ and Concat. Faster still, is using a custom IEnumerable Type-wrapper which stores references/pointers of passed arrays and allows looping over the entire collection as if it were a normal array. (Useful in HPC, Graphics Processing, Graphics render...)

Your Code:

var someStringArray = new[]{"a", "b", "c"};
var someStringArray2 = new[]{"d", "e", "f"};
someStringArray.Append(someStringArray2 ); //contains a,b,c,d,e,f

For the entire code and a generics version see: https://gist.github.com/lsauer/7919764

Note: This returns an unextended IEnumerable object. To return an extended object is a bit slower.

I compiled such extensions since 2002, with a lot of credits going to helpful people on CodeProject and 'Stackoverflow'. I will release these shortly and put the link up here.

Upvotes: 4

vikasse

Reputation: 455

int [] SouceArray1 = new int[] {2,1,3};
int [] SourceArray2 = new int[] {4,5,6};
int [] targetArray = new int [SouceArray1.Length + SourceArray2.Length];
SouceArray1.CopyTo(targetArray,0);
SourceArray2.CopyTo(targetArray,SouceArray1.Length) ; 
foreach (int i in targetArray) Console.WriteLine(i + " ");

Using the above code two Arrays can be easily merged.

Upvotes: 1

pasx

Reputation: 2975

Here is a simple example using Array.CopyTo. I think that it answers your question and gives an example of CopyTo usage - I am always puzzled when I need to use this function because the help is a bit unclear - the index is the position in the destination array where inserting occurs.

int[] xSrc1 = new int[3] { 0, 1, 2 };
int[] xSrc2 = new int[5] { 3, 4, 5, 6 , 7 };

int[] xAll = new int[xSrc1.Length + xSrc2.Length];
xSrc1.CopyTo(xAll, 0);
xSrc2.CopyTo(xAll, xSrc1.Length);

I guess you can't get it much simpler.

Upvotes: 2

WindyCityEagle

Reputation:

First, make sure you ask yourself the question "Should I really be using an Array here"?

Unless you're building something where speed is of the utmost importance, a typed List, like List<int> is probably the way to go. The only time I ever use arrays are for byte arrays when sending stuff over the network. Other than that, I never touch them.

Upvotes: 12

apandit

Reputation: 3344

I'm assuming you're using your own array types as opposed to the built-in .NET arrays:

public string[] merge(input1, input2)
{
    string[] output = new string[input1.length + input2.length];
    for(int i = 0; i < output.length; i++)
    {
        if (i >= input1.length)
            output[i] = input2[i-input1.length];
        else
            output[i] = input1[i];
    }
    return output;
}

Another way of doing this would be using the built in ArrayList class.

public ArrayList merge(input1, input2)
{
    Arraylist output = new ArrayList();
    foreach(string val in input1)
        output.add(val);
    foreach(string val in input2)
        output.add(val);
    return output;
}

Both examples are C#.

Upvotes: 0

GEOCHET

Reputation: 21313

I think you can use Array.Copy for this. It takes a source index and destination index so you should be able to append the one array to the other. If you need to go more complex than just appending one to the other, this may not be the right tool for you.

Upvotes: 7

Merging two arrays in .NET

Answers (28)

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