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C# how to do arithmetic operations on a 2d Array matrix

I've been toying with this code which prints a small matrix with negative and positive numbers,
I would like an efficient way to add together only the positive elements on the matrix and get the product of such elements also do the same but after a specific number, such as the highest on the matrix
static void Main(string[] args)
{
int row = 5;
int column = 5;
int[,] array = new int[row, column];
Random rand = new Random();
for (int i = 0; i < row; i++)
{
for (int j = 0; j < column; j++)
{
array[i, j] = rand.Next(-5, 10);
}
}
for (int i = 0; i < array.GetLength(0); i++)
{
for (int j = 0; j < array.GetLength(1); j++)
{
Console.Write(array[i, j].ToString() + " ");
}
Console.WriteLine(" ");
}
Console.ReadLine();
}

To filter and add positive matrix elements, you could do something like the following:
static void Main(string[] args)
{
const int rows = 5;
const int columns = 5;
var array = new int[rows, columns];
var rand = new Random();
int sum = 0;
bool numberSeen = false;
int numberToSee = 1;
for (int row = 0; row < rows; row++)
{
for (int col = 0; col < columns; col++)
{
var cell = rand.Next(-5, 10);
if (!numberSeen && (cell == numberToSee))
{
numberSeen = true;
}
array[row, col] = cell;
if (numberSeen && (cell > 0))
{
sum += cell;
}
}
}
Console.WriteLine($"sum = {sum}");
for (int row = 0; row < rows; row++)
{
for (int col = 0; col < columns; col++)
{
Console.Write(array[row, col].ToString() + " ");
}
Console.WriteLine(" ");
}
Console.ReadLine();
}

How to overcome this 2D -Transpose Matrix Index Out of Bound Exception in C# program

As you can see this is 2D transpose of matrix program, when executing this program it throws an index out of bound exception when it reached in some lines of code. Code raising exception is mentioned below.
C# Program
static void Main(string[] args)
{
Console.Write("No of Rows entered = ");
int r = Convert.ToInt32(Console.ReadLine());
Console.Write("No of Columns entered = ");
int c= Convert.ToInt32(Console.ReadLine());
int[,] arr1 = new int[r, c];
int[,] arr2 = new int[r, c];
for (int i = 0; i < r; i++)
{
for (int j = 0; j < c; j++)
{
Console.Write("[{0}],[{1}] : ", i, j+" ");
arr1[i, j] = Convert.ToInt32(Console.ReadLine());
}
}
Console.WriteLine("Matrix before Transpose:");
for (int i = 0; i < r; i++)
{
Console.WriteLine();
for (int j = 0; j < c; j++)
Console.Write("{0}", arr1[i, j]+" ");
}
```
**When it execute this lines of code it shows exception**
```
for (int i = 0; i < r; i++)
{
for (int j = 0; j < c; j++)
{
arr2[j, i] = arr1[i, j];
}
}
Console.WriteLine("Matrix after Transpose: ");
for (int i = 0; i < r; i++)
{
Console.WriteLine();
for (int j = 0; j < c; j++)
{
Console.Write("{0}", arr2[i, j]);
}
}
}
```
[Image of Exception appear while executing the program][1]
[1]: https://i.stack.imgur.com/6rNCg.png

The position of r and c should be changed in the definition of arr2:
int[,] arr2 = new int[c, r];
In the last for-loop, r and c should also be changed from position:
Console.WriteLine("Matrix after Transpose: ");
for (int i = 0; i < c; i++)
{
Console.WriteLine();
for (int j = 0; j < r; j++)
{
Console.Write("{0}", arr2[i, j]);
}
}

How to get all possible 2x2 sub matrices in a 3x3 matrix in C#?

If matrix A of size (3x3), then should i use the method of finding determinants, like grabbing the rows and column of first element and removing it from the array 2D array to get the remaining elements and then moving to the next element and repeating the same steps ?
[{1,2,3},
{4,5,6},
{7,8,9}]

I finally was able to do it, here's what I did :
enter image description here
class program
{
public static void Main()
{
int[,] arr = new int[3, 3];
Console.WriteLine("Enter elements of " + (arr.GetUpperBound(0) + 1) + "x" + (arr.GetUpperBound(1) + 1) + " matrix:");
for (int i = 0; i < (arr.GetUpperBound(0) + 1); i++)
{
for (int j = 0; j < (arr.GetUpperBound(1) + 1); j++)
{
arr[i, j] = Convert.ToInt32(Console.ReadLine());
}
}
Console.WriteLine("Matrix entered: ");
for (int i = 0; i < (arr.GetUpperBound(0) + 1); i++)
{
for (int j = 0; j < (arr.GetUpperBound(1) + 1); j++)
{
Console.Write("\t" + arr[i, j]);
}
Console.WriteLine();
}
Console.WriteLine("Possible sub-matrices: ");
for (int i = 0; i < 3; i++)
{
for (int j = 0; j< 3; j++)
{
TrimArray(i,j,arr);
}
}
}
public static int[,] TrimArray(int row, int column, int[,] original)
{
int[,] resultant = new int[original.GetLength(0) - 1, original.GetLength(1) - 1];
for (int i = 0, j = 0; i < original.GetLength(0); i++)
{
if (i == row)
continue;
for (int k = 0, u = 0; k < original.GetLength(1); k++)
{
if (k == column)
continue;
resultant[j, u] = original[i, k];
u++;
}
j++;
}
Console.WriteLine();
for (int i = 0; i < 2; i++)
{
for (int j = 0; j< 2; j++)
{
Console.Write("\t"+resultant[i,j]);
}
Console.WriteLine();
}
return resultant;
}
}

I did this for you yesterday, I created a method that will return a square matrix, given a parent matrix and the length.
static void Main(string[] args)
{
int[][] parentMatrix = new int[][]
{
new int [] { 1, 2, 3 },
new int [] { 4, 5, 6 },
new int [] { 7, 8, 9 }
};
var chunks = GetSubMatrices(parentMatrix, 2);
Console.WriteLine(chunks);
}
static List<int[][]> GetSubMatrices(int[][] parentMatrix, int m)
{
int n = parentMatrix.Length > m ? parentMatrix.Length : throw new InvalidOperationException("You can't use a matrix smaller than the chunk size");
var chunks = new List<int[][]>();
int movLimit = n - m + 1;
var allCount = Math.Pow(movLimit, 2);
for (int selRow = 0; selRow < movLimit; selRow ++)
{
for (int selCol = 0; selCol < movLimit; selCol ++)
{
// this is start position of the chunk
var chunk = new int[m][];
for (int row = 0; row < m; row++)
{
chunk[row] = new int[m];
for (int col = 0; col < m; col++)
{
chunk[row][col] = parentMatrix[selRow + row][selCol + col];
}
}
chunks.Add(chunk);
}
}
return chunks;
}
If you have any problems using it, you can simply comment below.

I needed to solve a problem like and came up with this answer. Hope it adds to your library of answers. If the submatrix specified is not greater than 1, do nothing.
public static void GetSubMatrixes(int[,] arr, int size)
{
int parentMatrixRowLength = arr.GetLength(0);
int parentMatrixColLength = arr.GetLength(1);
var overall = new List<object>();
if(size > 1)
{
for (int i = 0; i < parentMatrixRowLength; i++)
{
//get the columns
for (int j = 0; j < parentMatrixColLength; j++)
{
var subMatrix = new int[size, size];
/*if the new matrix starts from second to the last value in either the row(horizontal or column)
* do not proceed, go to the row or column in the parent matrix
* */
if (j < parentMatrixColLength - (size - 1) && i < parentMatrixRowLength - (size - 1))
{
//add
for (int m = 0; m < subMatrix.GetLength(0); m++)
{
for (int n = 0; n < subMatrix.GetLength(1); n++)
{
/*check the sum of current column value and the sum of the current row value
* of the parent column length and row length if it goes out of bounds
*/
var row = i + m; var col = j + n;
//actual check here
if (row < parentMatrixRowLength && col < parentMatrixColLength)
{
subMatrix[m, n] = arr[i + m, j + n];
}
}
}
overall.Add(subMatrix);
}
}
}
//display the sub matrixes here
for (int i = 0; i < overall.Count; i++)
{
var matrix = overall[i] as int[,];
for (int y = 0; y < matrix.GetLength(0); y++)
{
for (int x = 0; x < matrix.GetLength(1); x++)
{
Console.Write(string.Format("{0} ", matrix[y, x]));
}
Console.Write(Environment.NewLine + Environment.NewLine);
}
Console.WriteLine();
}
}
}

matrix, sub matrix with greatest sum

The task:
1. Make a matrix n by m and fill it with data from console.
2. Find the 3*3 sub matrix with the greatest sum.
{
static int[,] ArrayReadConsole()
{
Console.WriteLine("please enter n:");
int n;
n = Int32.Parse(Console.ReadLine());
Console.WriteLine("please enter m:");
int m;
m = Int32.Parse(Console.ReadLine());
int[,] data = new int[n, m];
for (int i = 0; i < n; i++)
{
for (int j = 0; j < m; j++)
{
Console.WriteLine("please enter a new value");
int number;
number = Int32.Parse(Console.ReadLine());
data[i, j] = number;
}
}
return data;
}
static void SumOfPlatform(int[,] data)
{
int sum =0;
int x = 0;
int y = 0;
int maxSum = 0;
for (int i = 0; i < data.GetLength(0) - 2; i++)
{
for (int j = 0; j < data.GetLength(1) - 2; j++)
{
for (int k = 0; k < 3; k++)
{
for (int l = 0; l < 3; l++)
{
sum =+ data[i + k, j + l];
}
}
if (maxSum < sum)
{
maxSum = sum;
x = i;
y = j;
}
sum =0;
}
}
Console.WriteLine("Sum: {0}\nPosition: {1} {2}",maxSum,x,y );
}
static void Main()
{
int[,] data = ArrayReadConsole();
SumOfPlatform(data);
}
}
}
I wrote that code but something went wrong... It doesn't find position or sum of the matrix I enter. I know that 4x for loop is a bad idea just I didn't want to make another method just for that. Any idea why it doesn't work?

Your Code for SumOfPlatform is working with only change from =+ to +=
static void SumOfPlatform(int[,] data)
{
int sum = 0;
int x = 0;
int y = 0;
int maxSum = 0;
for (int i = 0; i < data.GetLength(0) - 2; i++)
{
for (int j = 0; j < data.GetLength(1) - 2; j++)
{
for (int k = 0; k < 3; k++)
{
for (int l = 0; l < 3; l++)
{
sum += data[i + k, j + l]; //only Change
}
}
if (maxSum < sum)
{
maxSum = sum;
x = i;
y = j;
}
sum = 0;
}
}
Console.WriteLine("Sum: {0}\nPosition: {1} {2}", maxSum, x, y);
}
static void Main(string[] args)
{
// int[,] data = ArrayReadConsole();
int[,] data = new int[,]
{
{1,4,6,7,3,5,7,4 },
{1,4,5,3,3,5,4,4 },
{1,1,6,2,1,5,7,4 },
{1,3,6,3,3,5,2,4 },
{1,4,6,2,3,5,3,4 },
{1,4,2,2,3,5,3,4 },
{1,4,3,3,3,5,2,4 },
{1,4,4,3,3,5,2,4 }
};
SumOfPlatform(data);
}

Change 2d array bubble sort to counting sort

The following code sorts rows by the first element using bubble method.
I can't change it to counting sort.
public void SortStack(double[,] n)
{
for (int i = 0; i < n.GetLength(0) - 1; i++)
{
for (int j = i; j < n.GetLength(0); j++)
{
if (n[i, 0] > n[j, 0])
{
for (int k = 0; k < n.GetLength(1); k++)
{
var temp = n[i, k];
n[i, k] = n[j, k];
n[j, k] = temp;
}
}
}
}
}
Please help.

As you do bubble sort based on first element of each row. you should do counting sort like that too. so you just need to count first item of each row.
private static int[,] CountingSort2D(int[,] arr)
{
// find the max number by first item of each row
int max = arr[0, 0];
for (int i = 0; i < arr.GetLength(0); i++)
{
if (arr[i, 0] > max) max = arr[i, 0];
}
// we want to get count of first items of each row. thus we need 1d array.
int[] counts = new int[max + 1];
// do the counting. again on first index of each row
for (int i = 0; i < arr.GetLength(0); i++)
{
counts[arr[i, 0]]++;
}
for (int i = 1; i < counts.Length; i++)
{
counts[i] += counts[i - 1];
}
// result is sorted array
int[,] result = new int[arr.GetLength(0), arr.GetLength(1)];
for (int i = arr.GetLength(0) - 1; i >= 0; i--)
{
counts[arr[i, 0]]--;
// now we need to copy columns too. thus we need another loop
for (int j = 0; j < arr.GetLength(1); j++)
{
result[counts[arr[i, 0]], j] = arr[i, j];
}
}
return result;
}
Here is the test.
static void Main()
{
Random rand = new Random();
int[,] arr = new int[3,3];
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 3; j++)
{
arr[i, j] = rand.Next(0, 100);
}
}
int[,] newarr = CountingSort2D(arr);
for (int i = 0; i < arr.GetLength(0); i++)
{
Console.Write("{ ");
for (int j = 0; j < arr.GetLength(1); j++)
{
Console.Write(arr[i, j] + " ,");
}
Console.Write("} ,");
}
Console.WriteLine();
for (int i = 0; i < newarr.GetLength(0); i++)
{
Console.Write("{ ");
for (int j = 0; j < newarr.GetLength(1); j++)
{
Console.Write(newarr[i, j] + " ,");
}
Console.Write("} ,");
}
Console.WriteLine();
}
Example Output:
{ 49,66,8 },{ 33,39,64 },{ 65,52,76 } // Original array
{ 33,39,64 },{ 49,66,8 },{ 65,52,76 } // Sorted array