Splitting a 2D array into 4 smaller 2D arrays

Question

I need to loop through a 2D array of ints that is 4x4, but I also have to create 4 2x2 arrays out of it. Then I have to loop through each of those 4 2x2 arrays to pick out the average of the numbers in each 2x2 array.

    public int[,] Reduced(Sampler sampler)
    {
        int[,] a = new int[SampleSize,SampleSize];

        for (int r = 0; r < Math.Sqrt(image.Length); r+=SampleSize)
        {
            for (int c = 0; c < Math.Sqrt(image.Length); c+=SampleSize)
            {
                InsideLoop(a, r, c);                                   
            }
        }
        return a;
    }

    private void InsideLoop(int[,] a, int r, int c)
    {
        for (r = 0; r < SampleSize; r++)
        {
            for (c = 0; c < SampleSize; c++)
            {
                a[r, c] = image[r, c];
                Console.WriteLine("Value: {0}", a[r, c]);
            }
        }
    }

This is essentially what I've got so far, but it's working how it's written instead of how I'd like it to work. For this example, SampleSize is a variable that is set to 2. What this does currently is print out the numbers that create the first 2x2 array four times. My laptop battery is about to die, so I can't elborate more, but if anyone has any tips while I'm driving home. I had to finish posting this on my phone.

Answer 1

Generalized version:

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        int[,] original = new int[,] { {  1,  2,  3,  4 }, 
                                       {  5,  6,  7,  8 }, 
                                       {  9, 10, 11, 12 }, 
                                       { 13, 14, 15, 16 } };

        int[,] harder = new int[,] { {  1,  2,  3,  4,  5,  6,  7,  8,  9 },
                                     { 10, 11, 12, 13, 14, 15, 16, 17, 18 },
                                     { 19, 20, 21, 22, 23, 24, 25, 26, 27 },
                                     { 28, 29, 30, 31, 32, 33, 34, 35, 36 },
                                     { 37, 38, 39, 40, 41, 42, 43, 44, 45 },
                                     { 46, 47, 48, 49, 50, 51, 52, 53, 54 },
                                     { 55, 56, 57, 58, 59, 60, 61, 62, 63 },
                                     { 64, 65, 66, 67, 68, 69, 70, 71, 72 },
                                     { 73, 74, 75, 76, 77, 78, 79, 80, 81 } };

        IterateArray(original);
        Console.ReadLine();
    }

    static void IterateArray(int[,] array)
    {
        double tDim = Math.Sqrt(Math.Sqrt(array.Length));
        int dim = (int)tDim;
        if (dim != tDim) throw new ArgumentException("Not a valid array!");

        for (int i = 0; i < dim; i++)
        {
            IterateRows(array, dim, i);
        }
    }

    static void IterateRows(int[,] array, int dim, int pass)
    {
        int maxRow = dim * dim;
        IList<int> list = new List<int>(maxRow);
        for (int curRow = 0; curRow < maxRow; curRow++)
        {
            IterateColumns(array, dim, curRow, pass, list);
            if (list.Count == maxRow)
            {
                PrintNewArray(list, dim);
                list.Clear();
            }
        }
    }

    static void IterateColumns(int[,] array, int dim, int row, int pass, IList<int> list)
    {
        int maxCol = dim + (dim * pass);
        for (int curCol = pass * dim; curCol < maxCol; curCol++)
        {
            list.Add(array[row, curCol]);
        }
    }

    static void PrintNewArray(IList<int> list, int dim)
    {
        for(int i = 0; i < list.Count; i++)
        {
            if (i % dim == 0)
            {
                Console.WriteLine();
            }
            Console.Write($"{list[i]} ");
        }
        Console.WriteLine($"\nAverage {list.Average()}");
    }
}

Answer 2

Does this work?

int sampleSize = 2;
int[,] data = {
    {1, 2, 3, 4 },
    {5, 6, 7, 8 },
    {9, 10, 11, 12 },
    {13, 14, 15, 16 }
};

//assume input data is a perfect square as per your example
int max = (int)Math.Sqrt(data.Length);

List<int[,]> samples = new List<int[,]>();

int startX = 0;
while (startX + sampleSize <= max)
{
    int startY = 0;
    while (startY + sampleSize <= max)
    {
        int[,] sample = new int[sampleSize, sampleSize];
        for (int x = 0; x < sampleSize;x++)
        {
            for (int y = 0; y < sampleSize; y++)
            {
                sample[x, y] = data[x + startX, y + startY];
            }
        }
        samples.Add(sample);
        startY += sampleSize;
    }
    startX += sampleSize;
}

//for output testing
foreach (int[,] sample in samples)
{
    Console.WriteLine(sample[0, 0].ToString().PadLeft(2) + " | " + sample[0, 1]);
    Console.WriteLine(" -----  ");
    Console.WriteLine(sample[1, 0].ToString().PadLeft(2) + " | " + sample[1, 1]);
    Console.WriteLine();
    Console.WriteLine();

}
Console.ReadLine();

and here's the output

 1 | 2
 -----  
 5 | 6


 3 | 4
 -----  
 7 | 8


 9 | 10
 -----  
13 | 14


11 | 12
 -----  
15 | 16