C# Multidimensional Indexers

Last Updated : 06 Feb, 2025

In C#, indexers are special members that allow objects to be indexed similarly to arrays. Multi-dimensional indexers in C# are the same as multidimensional arrays. We can efficiently retrieve data with a multi-dimensional indexer by providing at least two parameters in its declaration. The first indexes the row dimension, the second indexes the column dimension, and so on.

Easy to implement multidimensional indexers in custom collections. We can easily use it to build custom operations.
We can define custom logic in the get and set accessors of the indexer to access or modify elements
Access elements using integer subscripts, each indexing a dimension

Example 1: This example shows Multidimensional Indexers using get and set accessors.

// C# program to illustrate the 
// Multidimensional Indexers 
using System;

class Geeks
{
    // reference to underlying 2D array 
    int[,] data = new int[5, 5];

    // declaring Multidimensional Indexer 
    public int this[int ind1, int ind2]
    {
        // get accessor 
        get
        {
            // it returns the values which 
            // read the indexes 
            return data[ind1, ind2];

        }

        // set accessor 
        set
        {
            // write the values in 'data' 
            // using value keyword 
            data[ind1, ind2] = value;
        }
    }
}

class main
{
    public static void Main(String[] args)
    {
        // creating the instance of 
        // Class Geeks as "ind" 
        Geeks ind = new Geeks();

        // assign the values accordingly to 
        // the indexes of the array 
        // 1st row 
        ind[0, 0] = 1;
        ind[0, 1] = 2;
        ind[0, 2] = 3;

        // 2nd row 
        ind[1, 0] = 4;
        ind[1, 1] = 5;
        ind[1, 2] = 6;

        // 3rd row 
        ind[2, 0] = 7;
        ind[2, 1] = 8;
        ind[2, 2] = 9;

        Console.WriteLine("{0}\t{1}\t{2}\n{3}\t{4}\t{5}\n{6}\t{7}\t{8}",
        ind[0, 0], ind[0, 1], ind[0, 2],
        ind[1, 0], ind[1, 1], ind[1, 2],
        ind[2, 0], ind[2, 1], ind[2, 2]);

    }
}

Output

1	2	3
4	5	6
7	8	9

Explanation: In the above example, we use a multidimensional indexer to access and modify elements in a 2D array. The get accessor retrieves values from the array, while the set accessor assigns values. The program fills the array and prints a 3x3 matrix.

Syntax of Multidimensional Indexer

public DataType this[DataType row, DataType column]
{
get { return data[row, column]; }
set { data[row, column] = value; }
}

get Accessor: It is used to retrieve the value at the defined indices.
set Accessor: It is used to assign a value to the defined indices.

Example 2: Demonstration of Multidimensional Indexer using only get(Read-Only) accessor.

// C# program to illustrate the Multidimensional 
// Indexer using get accessor 
using System;

class Geeks
{
    // default constructor 
    public Geeks() { }

    // Multidimensional Indexer 
    public int this[int i1, int i2]
    {
        // get accessor 
        get
        {
            // read only properties 
            return (i1 + i2);
        }

        // No set accessor used 
    }
    public static void Main(String[] args)
    {
        // creating object of class 
        // "Geeks" as "ind" 
        Geeks ind = new Geeks();

        // displaying the values 
        for (int i = 0; i <= 2; i++)
        {
            for (int j = 1; j <= 3; j++)
                Console.Write(ind[i, j] + "\t");

            Console.WriteLine();
        }
    }
}

Output

1	2	3	
2	3	4	
3	4	5

Explanation: In the above example, we use a read-only multidimensional indexer where the get accessor returns the sum of the given row and column indices. The program iterates over the indices and prints the calculated values in a tabular format.

Example 3: Demonstration of Multidimensional Indexer using only set accessor to modify elements.

// C# program to illustrate the 
// Multidimensional Indexer using set accessor
using System;

class Geeks
{
    // Private 2D array to store data
    private int[,] data = new int[3, 3];

    // Defining a multidimensional indexer
    public int this[int row, int column]
    {
        get
        {
            // Return the value at the 
            // specified row and column
            return data[row, column];
        }
        set
        {
            // Set the value at the 
            // specified row and column
            data[row, column] = value;
        }
    }

    static void Main(string[] args)
    {
        // Creating an instance 
        // of the Geeks class
        Geeks ind = new Geeks();

        // Assigning values using the indexer
        ind[0, 0] = 1;
 
        ind[1, 0] = 3;

        // Retrieving a value 
        // using the indexer
        int value = ind[1, 0];

        Console.WriteLine(value);
    }
}

Output

Explanation: In the above example, we use a multidimensional indexer with only a set accessor to assign values to a 2D array. The program sets specific values and retrieves one element to demonstrate the assignment operation.

Example 4: Custom Logic in the Get Accessor

In this example, we demonstrate how to incorporate custom logic in the get accessor of a multi-dimensional indexer. Let’s consider a scenario where we want to return a specific element based on the provided indices.

// Custom Logic in the Get Accessor
using System;

class Geeks
{
	public int this[int row, int column]
	{
		get
		{   // Custom logic
			if (row == 0 && column == 0)
				return 10;
			else if (row == 1 && column == 1)
				return 20;
			else if (row == 2 && column == 2)
				return 30;
			else
				return -1;
		}
	}
}

class main
{
	static void Main(string[] args)
	{
		Geeks ind = new Geeks();
		Console.WriteLine(ind[0, 0]); 
		Console.WriteLine(ind[1, 1]); 
		Console.WriteLine(ind[2, 2]); 
	}
}

Output

10
20
30

Explanation: In the above example, we use a multidimensional indexer with a custom get accessor that returns predefined values (10, 20, 30) for specific indices. If the indices do not match predefined cases, it returns -1. This demonstrates how to apply conditional logic inside an indexer.

C# - Overloading of Indexers

SoumikMondal

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Article Tags :

C# Multidimensional Indexers

Syntax of Multidimensional Indexer

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