For in Javascript Array 3d

Question

I want initialize an array 3d with zeros in all positions. i am using a for cycle for filling my matrix but when I tested, I get an error TypeError: this.matrix[x][y] is undefined I have this:

class Cube {
 constructor(size) {
 this.size = size
 this.matrix = [ [ [] ], [ [] ] ]
 this.createMatrix(size)
 }
 getsize() {
 return this.size
 }
 /*Fill matrix with zeros*/
 createMatrix(size) {
 for (var x = 0; x < size; x++) {
 for (var y = 0; y < size ; y++) {
 for (var z = 0; z < size ; z++) {
 this.matrix[x][y][z] = 0
 }
 } 
 }
 console.log(this.matrix)
 }
 }
 myCube = new Cube(4)

How Can I fill my matrix?

Answer 1

You will have to check every item in the array if it wasn't initialized yet, and in such case you will need to set it to Array:

class Cube {
 constructor(size) {
 this.size = size
 this.matrix = [ ]
 this.createMatrix(size)
 }
 getsize() {
 return this.size
 }
 /*Fill matrix with zeros*/
 createMatrix(size) {
 for (var x = 0; x < size; x++) {
 for (var y = 0; y < size ; y++) {
 for (var z = 0; z < size ; z++) {
 if (!Array.isArray(this.matrix[x])) {
 this.matrix[x] = []
 }
 if (!Array.isArray(this.matrix[x][y])) {
 this.matrix[x][y] = []
 }
 if (!Array.isArray(this.matrix[x][y][z])) {
 this.matrix[x][y][z]= []
 }
 this.matrix[x][y][z] = 0
 }
 } 
 }
 console.log(this.matrix)
 }
}
myCube = new Cube(4)

• Mike Cluck: Note: typeof is not a function so parentheses are not required and typeof [] will return "object" so it's not a good method for checking if something is an array.
• Dekel: @MikeC thanks for the comment! Changed to Array.isArray instead of typeof
• Carmoreno: Thanks @Dekel, your answer was useful for me.

Answer 2

That's because you need to initialize each individual array. Remember: a 3D array is an array of arrays of arrays.

function threeDArray(width, height, depth) {
 var result = [];
 for (var x = 0; x < width; x++) {
 result[x] = [];
 for (var y = 0; y < height; y++) {
 result[x][y] = [];
 for (var z = 0; z < depth; z++) {
 result[x][y][z] = 0;
 }
 }
 }
 return result;
}
console.log(threeDArray(3, 3, 3));

Answer 3

You can use Array.from({ length: n }) to create empty arrays of n length, and fill them with zeros using the fill() method:

const emptyArray = n => Array.from({ length: n });
const createMatrix = n => emptyArray(n).map(() =>
 emptyArray(n).map(() => emptyArray(n).fill(0))
);
console.log(createMatrix(4));