Initializing and filling multi dimension array in javascript

Question

How do we initialize and create new multi dimension array?

Let's imagine if I want to initialize a 4x4 multi dimension array and fill it with 0's

Ideally, in 2D arrays, we would do

let oned_array = new Array(10).fill(0); // would create array of size 10 and fill it up with 0

How would I do something like [[0,0], [0,0]] (2x2 matrix)

let matrix = new Array([]).fill(0);

I'm trying to solve few algorithm problems and this requires me creating a new multi dimension array and going through them (Island problem etc)

Please advise.

EDIT:

Another solution I found:

Array(2).fill(0).map(_ => Array(2).fill(0));

did you aware that recommended identifier name format [a-zA-z][a-zA-Z0-9_]+ — Sagar V
– Sagar V, Commented Aug 22, 2017 at 18:56
@Redo thank you for your response. Can you elucidate further? I'm trying to understand what you meant by 'identifier name format' can you state an example? — TechnoCorner
– TechnoCorner, Commented Aug 22, 2017 at 19:21
avoid using variables such as 1Darray that is starting with a non alpha character. most of the languages will give you error — Sagar V
– Sagar V, Commented Aug 22, 2017 at 19:22
Possible duplicate of How can I create a two dimensional array in JavaScript? — rphv
– rphv, Commented Aug 22, 2017 at 19:23

Nina Scholz · Accepted Answer · 2017-08-22 19:12:52Z

3

To get an independent filled array, you could use Array.from and map a new array with mapped values.

var array = Array.from({ length: 4 }, _ => Array.from({ length: 4 }, _ => 4));

array[0][0] = 0;
console.log(array);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Aug 22, 2017 at 19:12

Nina Scholz

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2 Comments

TechnoCorner Over a year ago

Can we do something like ` a = Array(5).fill(0).map(x => Array(10).fill(0))` But my question was instead of looping through an array and creating another, can't we have a shorthand like .fill to create/fill mutli dimension arrays?

Nina Scholz Over a year ago

actually fill uses a value for every element, if that is an array, you insert the same object reference.

user4639281 · Accepted Answer · 2017-08-22 19:44:08Z

2

@NinaScholz' answer is much better—as always—but I finished writing this before seeing that answer so have decided to post anyway.

Similar idea but without the use of Array.from. It creates a new array at the specified length, fills it with 0's so that it can be iterated, iterates it to replace 0's with a new array of the specified length filled with the specified value.

    
const buildMatrix = (l, h, v) => Array(l).fill(0).map(_ => Array(h).fill(v));
const matrix = buildMatrix(4,4,4);
matrix[0][0] = 0;
console.log(matrix);

.as-console-wrapper { max-height: 100% !important; }

answered Aug 22, 2017 at 19:44

user4639281

2 Comments

TechnoCorner Over a year ago

Thanks for your post. Can i re-write this to var test2 = new Array(2).fill(new Array(2).fill(0))

user4639281 Over a year ago

It would be Array(2).fill(0).map(_ => Array(2).fill(0)); The map is important, otherwise it would fill the array with references to the same array, instead of creating a new array for each element.

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