Return an n*n nested array populated with null

Question

I'm very lost here. Given a number, n, I have to return an n*n nested array populated with the value null. If n is 3:

[
  [null, null, null],
  [null, null, null],
  [null, null, null]
]

I am so lost. I've got something like this:

function generateMatrix (n) {
  let item = 'null';
  let array1 = [];
  let solution = [];
  array1.push(item.repeat(n));
  solution.push(array1.repeat(n));
  return solution;  
  }

I know it isn't right, not only because it's not working, but also because it doesn't make sense and I don't know how to do it. Bear in mind I'm very very junior, just started learning JS.

I've seen other similar threads, but can't figure it out.

Thanks in advance.

So given *n* - you need to loop that many times. Inside each loop, you need to loop again — tymeJV, Mar 26 '18 at 21:12
You want to first be able to create a row of n `null` - there are various ways such as loops, or you can use `Array.fill` (which loops the array internally), in combination with `Array(n)` which creates an array of length n containing `undefined` but uses `.fill` to change them to `null`, as in the below answer, to output `[null, null, null]` (if n is 3) and then use this same pattern to create a row of rows. So you would fill an array with n `[null, null, null]` to get the matrix you described. — George, Mar 26 '18 at 21:21

Nenad Vracar · Answer 1 · 2018-03-26T21:20:49.880

4

You could do this with Array.from and Array.fill methods.

function matrix(n) {
  return Array.from(Array(n), () => Array(n).fill(null))
}

console.log(matrix(3))

You can use the same approach to create matrix with rows x columns dimensions.

function matrix(rows, cols) {
  return Array.from(Array(rows), () => Array(cols).fill(null))
}

console.log(matrix(2, 4))
console.log(matrix(3, 2))

edited Mar 26 '18 at 21:20

answered Mar 26 '18 at 21:12

Nenad Vracar

118,580
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151
176

score 3 · Accepted Answer · answered Mar 26 '18 at 21:13

3

function generateMatrix (n) {
  let result = [];
  for (var i = 0; i < n; i++) {
    result.push([]);
    for (var j = 0; j < n; j++) {
      result[i].push(null);
    }
  }
  return result;  
}
console.log(generateMatrix(3));

answered Mar 26 '18 at 21:13

Igor

15,833
1
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score 1 · Answer 3 · edited Jun 20 '20 at 09:12

This is an alternative using the function Array.from and the function fill.

var rows = 3;
var cols = 3;

var matrix = Array.from({length: rows}, () => new Array(cols).fill(null))
console.log(JSON.stringify(matrix, null, 2));

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

Array.from

Array.from() lets you create Arrays from:

array-like objects (objects with a length property and indexed elements) or

iterable objects (objects where you can get its elements, such as Map and Set).

Return an n*n nested array populated with null

3 Answers3

Array.from