Jagged arrays

Jagged arrays are arrays that instead of primitive types, contain arrays (or other collections). It’s like an array of arrays - each array element contains another array. They are similar to multidimensional arrays, but have a slight difference - as multidimensional arrays are limited to a fixed number of rows and columns, with jagged arrays, every row can have a different number of columns.

Declaring a jagged array

For example, declaring a jagged array with 8 columns:

int[][] a = new int[8][];

The second [] is initialized without a number. To initialize the sub arrays, you would need to do that separately:

for (int i = 0; i < a.length; i++) 
{
    a[i] = new int[10];
}

Getting/Setting values

Now, getting one of the subarrays is easy. Let’s print all the numbers of the 3rd column of a:

for (int i = 0; i < a[2].length; i++)
{
    Console.WriteLine(a[2][i]);
}

Getting a specific value:

a[<row_number>][<column_number>]

Setting a specific value:

a[<row_number>][<column_number>] = <value>

Remember: It’s always recommended to use jagged arrays (arrays of arrays) rather than multidimensional arrays (matrixes). It’s faster and safer to use.

Note on the order of the brackets

Consider a three-dimensional array of five-dimensional arrays of one-dimensional arrays of int. This is written in C# as:

int[,,][,,,,][] arr = new int[8, 10, 12][,,,,][];

In the CLR type system, the convention for the ordering of the brackets is reversed, so with the above arr instance we have:

arr.GetType().ToString() == "System.Int32[][,,,,][,,]"

and likewise:

typeof(int[,,][,,,,][]).ToString() == "System.Int32[][,,,,][,,]"