How to optimize function for merging sorted arrays in C#

Question

I write this function for merging two arrays.

private static int[] Merge(int[] array1, int[] array2)
{
    var mergedArray = new int[array1.Length + array2.Length];
    int i = 0, j = 0, k = 0;
    while(k < mergedArray.Length)
    {
        if(i == array1.Length || j == array2.Length)
        {
             if (i <= j)
                {
                    mergedArray[k] = array1[i];
                    i++;
                }
                else
                {
                    mergedArray[k] = array2[j];
                    j++;
                }
        }
        else
        {
            if(array1[i] < array2[j])
            {
                mergedArray[k] = array1[i];
                i++;
            }
            else
            {
                mergedArray[k] = array2[j];
                j++;
            }
        }
        k++;
    }
    return mergedArray;
}

How to reduce if statements in this code?

Answer 1

You can also make a Linq friendly version. This one is fast and will work on IEnumerable. You could easily translate this to any type T where T is IComparable.

    private static IEnumerable<int> Merge(IEnumerable<int> enum1, IEnumerable<int> enum2)
    {
        IEnumerator<int> e1 = enum1.GetEnumerator();
        IEnumerator<int> e2 = enum2.GetEnumerator();

        bool remaining1 = e1.MoveNext();
        bool remaining2 = e2.MoveNext();

        while (remaining1 || remaining2)
        {
            if (remaining1 && remaining2)
            {
                if (e1.Current > e2.Current)
                {
                    yield return e2.Current;
                    remaining2 = e2.MoveNext();
                }
                else
                {
                    yield return e1.Current;
                    remaining1 = e1.MoveNext();
                }
            }
            else if (remaining2)
            {
                yield return e2.Current;
                remaining2 = e2.MoveNext();
            }
            else
            {
                yield return e1.Current;
                remaining1 = e1.MoveNext();
            }
        }
    }

Answer 2

Not as good as the Linq solution, but if you want the traditional if-then style function you could write:

private static int[] Merge(int[] array1, int[] array2)
{
    var mergedArray = new int[array1.Length + array2.Length];
    int i = 0, j = 0, k = 0;
    while(k < mergedArray.Length)
    {
        if (j == array2.Length || ((i < array1.Length) && (array[i] < array2[j])))
        {
            mergedArray[k] = array1[i];
            i++;
        }
        else
        {
            mergedArray[k] = array2[j];
            j++;
        }
        k++;
    }
    return mergedArray;
}

(edit: missing brace added)

Or in English:

If array2 is empty or if there are still values in array 1 and array1[i] is less than array2[j], then take value from array1, otherwise take from array 2

Or very concise (just for fun):

private static int[] Merge(int[] array1, int[] array2)
{
    var mergedArray = new int[array1.Length + array2.Length];
    int i = 0, j = 0;
    while(i+j < mergedArray.Length)
        if (j == array2.Length || ((i < array1.Length) && (array1[i] < array2[j])))
            mergedArray[i+j] = array1[i++];
        else
            mergedArray[i+j] = array2[j++];
    return mergedArray;
}