Jagged array

In computer science, a jagged array, also known as a ragged array ^[1] or irregular array ^[2] is an array of arrays of which the member arrays can be of different lengths,^[3] producing rows of jagged edges when visualized as output. In contrast, two-dimensional arrays are always rectangular^[4] so jagged arrays should not be confused with multidimensional arrays, but the former is often used to emulate the latter.

Memory layout of a jagged array.

Arrays of arrays in languages such as Java, PHP, Python (multidimensional lists), Ruby, C#.NET, Visual Basic.NET, Perl, JavaScript, Objective-C, Swift, and Atlas Autocode are implemented as Iliffe vectors.

Examples

In C# and Java^[5] jagged arrays can be created with the following code:^[6]

int[][] c;
c = new int[2][]; // creates 2 rows
c[0] = new int[5]; // 5 columns for row 0
c[1] = new int[3]; // create 3 columns for row 1

In C and C++, a jagged array can be created (on the stack) using the following code:

int jagged_row0[] = {0,1};
int jagged_row1[] = {1,2,3};
int *jagged[] = { jagged_row0, jagged_row1 };

In C/C++, jagged arrays can also be created (on the heap) with an array of pointers:

int *jagged[5];

jagged[0] = malloc(sizeof(int) * 10);
jagged[1] = malloc(sizeof(int) * 3);

In C++/CLI, jagged array can be created with the code:^[7]

using namespace System;
int main()
{
    array<array<double> ^> ^ Arrayname = gcnew array <array<double> ^> (4); // array contains 4 
    //elements
    return 0;
}

In Fortran, a jagged array can be created using derived types with allocatable component(s):

type :: Jagged_type
    integer, allocatable :: row(:)
end type Jagged_type
type(Jagged_type) :: Jagged(3)
Jagged(1)%row = [1]
Jagged(2)%row = [1,2]
Jagged(3)%row = [1,2,3]

In Python, jagged arrays are not native but one can use list comprehensions to create a multi-dimensional list which supports any dimensional matrix:^[8]

multi_list_3d = [[[] for i in range(3)] for i in range(3)]
# Produces: [[[], [], []], [[], [], []], [[], [], []]]

multi_list_5d = [[[] for i in range(5)] for i in range(5)]
# Produces: [[[], [], [], [], []], [[], [], [], [], []], [[], [], [], [], []], [[], [], [], [], []], [[], [], [], [], []]]

See also

• Variable-length array
• Iliffe vector