1

Problem

I am writing a Matrix class in C# and I know that this class needs a two dimension array to store the Matrix object. The constructor for my Matrix class takes two parameters, the m and n dimensions of the Matrix. I have tried to assign the array inside the constructor but I get the error that Invalid Rank Specifier. The code I tried is listed below.

class Matrix
    {
        //make the dimensions private
        private int m,n;

        //The Matrix constructor needs two parameters
        //The row and column dimensions
        //declare the two dimension array
        private int[][] array;
        public Matrix(int m, int n) {
          //assign the array inside the constructor
            array = new int[m][n];
        }
        //method to allocate the Matrix
    }

My goal is to initialize the array with the dimensions first so that assigning can be done without errors, Thank You.
Improve this question
4
  • 1
    First option is use a multidimensional array instead of a jagged array, Second, use a loop to allocate each leaf array Commented Nov 3, 2021 at 7:49
  • @ChrᴉzremembersMonica, but I just initialized to it using the new keyword following the array that needs to be stored in that object Commented Nov 3, 2021 at 7:51
  • 2
    See also here: jagged vs multidimensional Commented Nov 3, 2021 at 7:52
  • @ChrᴉzremembersMonica, opened the link, its the same exact problem , Thanks. Commented Nov 3, 2021 at 7:54

3 Answers 3

Reset to default
3

I feel like what you are trying to do is create a multi dimensional array, which you can learn more about here.

In your case this would mean that you would create an int[,] array as such:

class Matrix
{
    //make the dimensions private
    private int m,n;

    //The Matrix constructor needs two parameters
    //The row and column dimensions
    //declare the two dimension array
    private int[,] array;
    public Matrix(int m, int n) {
      //assign the array inside the constructor
        array = new int[m, n];
    }
    //method to allocate the Matrix
}

After that you can access your values through:

public int GetValue(int m, int n) => array[m,n];

And equally for settings values:

public void SetValue(int m, int n) => array[m,n] = value;
Improve this answer
Sign up to request clarification or add additional context in comments.

4 Comments

Okay, can you edit the method for setting values to use a loop, i just want to understand how the iteration is performed to achieve a successful assignment
I tried to assign after creating a new Matrix object and i got an error that cannot apply indexing with [] to an object of type Matrix. I tried to assign like this Matrix A = new Matrix(4,4); A[0][0]=2;Can you help me figure out why that is?
If you want to iterate through a multidimension array you can do: for(int i = 0; i <= array.GetUpperBound(0); i++) { Console.WriteLine(array[i,0]) } However if you want to iterate through all of dimensions and all elements you can do something likes this: for(int i = 0; i < array.GetLength(0); i++) for(int x = 0; x < array.GetLength(1); x++)
@RóbertPécz, did you check the constructor in my Matrix class?The constructor is everything, I will use that to initialize the array outside the class
1

You actually have a jagged array, i.e. array of array: int[][], note that 2d array is int[,]

To initialize int[][] you have to create each inner array:

 public Matrix(int m, int n) {
   array = new int[m][];         // outer array of size m which

   for (int i = 0; i < n; ++i)   // contains
     array[i] = new int[n];      // arrays of length n 
 }

You can use Linq for shorter syntax:

 using System.Linq;

 ...

 public Matrix(int m, int n) {
   array = Enumerable
     .Range(0, m)
     .Select(_ => new int[n])
     .ToArray();
 }

Edit: Possible Matrix implementation:

  class Matrix {
    private int[][] array;

    public Matrix(int rows, int columns) {
      if (rows <= 0)
        throw new ArgumentOutOfRangeException(nameof(rows));
      if (columns <= 0)
        throw new ArgumentOutOfRangeException(nameof(columns));

      array = Enumerable
        .Range(0, rows)
        .Select(_ => new int[columns])
        .ToArray();
    }

    public int RowCount => array.Length;

    public int ColumnCount => array[0].Length;

    public int this[int row, int column] {
      get {
        if (row < 0 || row >= array.Length)
          throw new ArgumentOutOfRangeException(nameof(row));
        if (column < 0 || column >= array[row].Length)
          throw new ArgumentOutOfRangeException(nameof(column));

        return array[row][column];
      }
      set {
        if (row < 0 || row >= array.Length)
          throw new ArgumentOutOfRangeException(nameof(row));
        if (column < 0 || column >= array[row].Length)
          throw new ArgumentOutOfRangeException(nameof(column));

        array[row][column] = value;
      }
    }
  }
Improve this answer

10 Comments

What is a jagged array?
Am trying to assign to the array and am getting this error, Cannot apply indexing with [] to an object of type Matrix, I tried assigning to a certain index like this Matrix A = new Matrix(4,4); A[0][0]
@KINYUA TIMOTHY NJIRU: jagged array is an array of arrays: note that inner arrays can be of different lengths: int[][] array = new int[][] {new int[] {1, 2, 3}, new int[] {4}, new int[] {5, 6}};
recheck my first comment, am getting an error trying to assign after creating a 4 by 4 array Matrix
Okay, my bad, l need to access the array inside the Matrix object and assign, How do we assign multidimension arrays?
|
1

I prefer to use a regular 1D array for 2D data. Something like:

public class MyMatrix<T> 
{
        public int Width { get; }
        public int Height { get; }
        public T[] Data { get; }
        public MyMatrix(int width, int height)
        {
            Width = width;
            Height = height;
            Data = new T[width * height];
        }
        public T this[int x, int y]
        {
            get => Data[y * Width + x];
            set => Data[y * Width + x] = value;
        }
}

This has some advantages over the typical 2D Multidimensional approach:

  • Interoperability: Multidimensional arrays are a .Net concept that does not exist in every language, but just about every language have some sort of 1D array.
  • Serialization: Most serialization libraries handle 1D arrays, support for 2D arrays are more spotty.
  • Performance: Sometimes you just need to iterate over all the items, using the backing 1D arrays is probably the fastest way to do this.
  • Avoiding pitfals: .GetLength() for multidimensional arrays is quite slow, not a large problem if you cache the values outside your loop, but can be a problem if you do not know about this, or forget.
Improve this answer

5 Comments

Wow, trying this out, looks safe and easy to implement, am having an issue with the assignment of a certain index A[0][0] in the array, compiler says cannot apply indexing with [] to an object of type Matrix, I hope your code will work.
What version of .Net does this run on again, am getting an error in the getters and setters that only specific assignment, call, increment, decrement, call can be used as statement
@KINYUA TIMOTHY NJIRU indexing is done like [x, y] not [x][y]. Not sure about the error, but it will require c# 7 for the expression bodied properties, but you should be able to just use regular setters/getters. I.e. get{return Data[y * Width + x];}
you know you need to edit your answer so it becomes easier for me
@KINYUA TIMOTHY NJIRU the example code is perfectly fine as it is in any recent version of c#. I do not see it as very helpful overall to use examples using first version of the language since it lacks even basic features like generics.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.