Programmatically Declare Array of Arbitrary Rank

Question

In C#, there are three types of arrays: one-dimensional, jagged, and multi-dimensional rectangular.

The question is: given an array of a specific size, how can we cr

Answer 1

Use Array.CreateInstance(Type, Int32[]) method to create an array of an arbitrary size.

But the problem, you will have after creating this array is: How do you efficiently access the elements of the array if you don't know its rank?

You may use myArray.GetValue(Int32[]) and myArray.SetValue(Object, Int32[]) but I assume the performance is no that good.

To sum up:

public static Array CreateArray(Array array)
{
    // Gets the lengths and lower bounds of the input array
    int[] lowerBounds = new int[array.Rank];
    int[] lengths = new int[array.Rank];
    for (int numDimension = 0; numDimension < array.Rank; numDimension++)
    {
        lowerBounds[numDimension] = array.GetLowerBound(numDimension);
        lengths[numDimension] = array.GetLength(numDimension);
    }

    Type elementType = array.GetType().GetElementType();  // Gets the type of the elements in the input array

    return Array.CreateInstance(elementType, lengths, lowerBounds);    // Returns the new array
}

Update

I've done a little benchmark to compare performance of the array indexer and the GetValue, SetValue versions.

Here is the code I used:

const int size = 10000000;
object[] array1 = new object[size];
object[] array2 = new object[size];

Random random;
random = new Random(0);
for (int i = 0; i < size; i++)
{
    array1[i] = random.Next();
    array2[i] = random.Next();
}

Stopwatch stopwatch = new Stopwatch();

Console.ReadKey();
stopwatch.Restart();
for (int i = 0; i < size; i++)
    array1[i] = array2[i];
stopwatch.Stop();
Console.WriteLine("Indexer method: {0}", stopwatch.Elapsed);

random = new Random(0);
for (int i = 0; i < size; i++)
{
    array1[i] = random.Next();
    array2[i] = random.Next();
}

Console.ReadKey();
stopwatch.Restart();
for (int i = 0; i < size; i++)
    array1.SetValue(array2.GetValue(i), i);
stopwatch.Stop();
Console.WriteLine("Get/SetValue method: {0}", stopwatch.Elapsed);

The result are:

Indexer method: 0.014 s
Set/GetValue method: 1.33 s

The result are slightly different if I replace the int by object.

Indexer method: 0.05 s
Set/GetValue method: 0.54 s

This can be easily explained by the necessary boxing/unboxing when using integer with Set/GetValue.