Multidimensional arrays

Learn to create matrix-like structures with nested arrays.

Nested arrays

The elements of an array can themselves be arrays. This is called a nested array. It is used to store data shaped like a two-dimensional grid.

Example: const grid = [[1, 2, 3], [4, 5, 6]]; is a matrix with two rows. The first row is grid[0], the second row is grid[1].

To access a cell you use two indices: grid[0][1] returns the second element of the first row (2).

Traversing with nested loops

To traverse a nested array you use a nested for loop. The outer loop visits rows, the inner loop visits columns.

Example: for (let i = 0; i < grid.length; i++) { for (let j = 0; j < grid[i].length; j++) { console.log(grid[i][j]); } } prints every cell in order.

grid.length gives the row count, grid[i].length gives the column count of one row. In a regular matrix these are the row and column counts.

Exercise Print a cell from the matrix array

Create a nested array named matrix with at least two rows. Each row must hold at least three numbers. Then print the third element of the second row (matrix[1][2]) with console.log.

Show example solution

Define a matrix array with two rows of three numbers, then print matrix[1][2].
Example solution:
const matrix = [[1, 2, 3], [4, 5, 6]];
console.log(matrix[1][2]);

Test yourself

What value does <code>grid[2][1]</code> return?
```
const grid = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
```
- 2
- 5
- 8
- 6
Show answer

8 — Correct. grid[2] is the third row [7, 8, 9]; grid[2][1] returns 8.

Access a cell with grid[1][2]

const grid = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
const cell = grid[1][____];
console.log(cell);

Show answer

const grid = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
const cell = grid[1][2];
console.log(cell);

Match expressions for <code>const grid = [[1, 2, 3], [4, 5, 6]]</code>

grid.length

2
grid[0]

[1, 2, 3]
grid[1][0]

4
grid[0][2]

3

Next lesson: Summary - Array basics

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies