C# A nested array initializer is expected, build 3dimensional array using a 2dimensional array

Question

From a function I am receiving a 2 dimensional array, I want to use this array as input data to my neural network. For this to be working it has to be an element of a 3-dimensional array. When I try to do this I get an error. I'm probably doing something wrong syntax-wise but can't figure out what the solution is. Can anyone help me?

int[,] d = image.GetData();
int[,,] neuralInput = { { d } };

also tried:

int[,,] neuralInput = { d };
bool[] answers = new bool[1] { true };

which both result in this error:

Severity    Code    Description Project File    Line    Suppression State
Error   CS0846  A nested array initializer is expected  Sandbox C:\Users\Jordy\Documents\KBS-SE3_VR- 
Rehabilitation-Data\Sandbox\Program.cs  47  Active

and:

int[,] d = image.GetData();
int[,,] neuralInput;
neuralInput[0] = d;

which results in:

Severity    Code    Description Project File    Line    Suppression State
Error   CS0022  Wrong number of indices inside []; expected 3   Sandbox C:\Users\Jordy\Documents\KBS- 
SE3_VR-Rehabilitation-Data\Sandbox\Program.cs   47  Active

Jon Skeet · Accepted Answer · 2019-12-16 14:59:00Z

Every element of an int[,,] is an int - they're independent elements. It looks like what you're trying to build is an int[][,] - an array where each element is an int[,]. If you genuinely need an int[,,], you'll need to create one of the right size, and copy elements from your int[,] into it. It's possible that Buffer.BlockCopy or similar would do that, but I'd probably just write a loop... something like this:

public int[,,] Project2DInto3D(int[,] source)
{
    int cols = source.GetLength(0);
    int rows = source.GetLength(1);
    int[,,] ret = new int[1, cols, rows];
    for (int x = 0; x < cols; x++)
    {
        for (int y = 0; y < rows; y++)
        {
            ret[0, x, y] = source[x, y];
        }
    }
    return ret;
}

Full example:

using System;

public class Test
{
    public static void Main()
    {
        int[,] original = { { 5, 3 }, { 2, 1 }, { 8, 3 } };
        Console.WriteLine("Original:");
        for (int j = 0; j < 3; j++)
        {
            for (int k = 0; k < 2; k++)
            {
                Console.WriteLine($"[{j}, {k}] = {original[j, k]}");
            }
        }
        Console.WriteLine();

        var projected = Project2DInto3D(original);
        Console.WriteLine("Projected:");
        for (int i = 0; i < 1; i++)
        {
            for (int j = 0; j < 3; j++)
            {
                for (int k = 0; k < 2; k++)
                {
                    Console.WriteLine($"[{i}, {j}, {k}] = {projected[i, j, k]}");
                }
            }
        }
    }

    public static int[,,] Project2DInto3D(int[,] source)
    {
        int cols = source.GetLength(0);
        int rows = source.GetLength(1);
        int[,,] ret = new int[1, cols, rows];
        for (int x = 0; x < cols; x++)
        {
            for (int y = 0; y < rows; y++)
            {
                ret[0, x, y] = source[x, y];
            }
        }
        return ret;
    }
}

Output:

Original:
[0, 0] = 5
[0, 1] = 3
[1, 0] = 2
[1, 1] = 1
[2, 0] = 8
[2, 1] = 3

Projected:
[0, 0, 0] = 5
[0, 0, 1] = 3
[0, 1, 0] = 2
[0, 1, 1] = 1
[0, 2, 0] = 8
[0, 2, 1] = 3

Kritner · Accepted Answer · 2019-12-16 14:52:20Z

0

You've attempted to provide array initializers for both a single dimensional:

int[,,] neuralInput = { d }; // states 3 dimensions, initialized as one, invalid.

and two dimensional:

int[,,] neuralInput = { { d } };  // states 3 dimensions, (almost) initialized as two, invalid.

but no three dimensional:

int[, ,] array3D = new int[,,] { { { 1, 2, 3 }, { 4, 5, 6 } }, { { 7, 8, 9 }, { 10, 11, 12 } } };

more:

Multidimensional Arrays (C# Programming Guide)

answered Dec 16, 2019 at 14:52

Kritner

13.8k11 gold badges53 silver badges76 bronze badges

Comments

CoderCharmander · Accepted Answer · 2019-12-16 14:56:19Z

0

There are differences in C# between jagged and multi-dimensional arrays. The jagged arrays are arrays in arrays, and can be declared like that:

int[][] jagged2d = new int[][];

Jagged arrays are arrays in arrays. If you used a jagged array, it would work. You can set one of its inner arrays.

However, "simple" multi-dimensional arrays aren't meant to modify a full array inside them; you can only modify or get exactly one value at a time.

For more information, refer to jagged arrays and multidimensional arrays.

answered Dec 16, 2019 at 14:56

CoderCharmander

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