For-Loop to Generate Multi Dimensional Array

Question

thank you in advance for taking the time to help me with this question.

I am trying to generate a simple board like so, using a for loop.

var board = [[0,0,0,0,0,0,0,0],[0,0,0,0,0,0,0,0],[0,0,0,0,0,0,0,0],
[0,0,0,0,0,0,0,0],[0,0,0,0,0,0,0,0],[0,0,0,0,0,0,0,0],
[0,0,0,0,0,0,0,0],[0,0,0,0,0,0,0,0]];

However, my attempt below has not been successful.

function makeBoard(n){
  var board=[];
  for(var i=0; i<n; i++){
    for(var j=0; j<n; j++){
      board[i][j]=0;
    }
  }
  return board;
}

Technically, I could just use the board variable I have shown above, and continue, but I am more concerned with the principle. Is it not possible to create a multidimensional array using for loop? Is there a simple way to accomplish this using array.push()?

Paul · Accepted Answer · 2016-04-07 19:24:31Z

3

JavaScript doesn't have multidimensional arrays, so you have to use an array of arrays instead:

function makeBoard(n){
  var board=[];
  for(var i=0; i<n; i++){
    board[i] = [];
    for(var j=0; j<n; j++){
      board[i][j]=0;
    }
  }
  return board;
}

You were missing the board[i] = []; needed to create each array for the second dimension.

Note: You could also use Array.prototype.fill:

function makeBoard(n){
  var board=[];
  for(var i=0; i<n; i++){
    board[i] = Array(n).fill( 0 );
  }
  return board;
}

answered Apr 7, 2016 at 19:24

Paul

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2 Comments

Nina Scholz Over a year ago

fill works only on selected user agents.

Paul Over a year ago

@isvforall That doesn't work, since Array.fill doesn't do a deep copy. You end up with board[0] === board[1] === board[2] ... all references to the same array

Nina Scholz · Accepted Answer · 2016-04-07 19:35:22Z

1

You need for every new sub array an initialisation as array:

function makeBoard(n){
    var board=[];
    for(var i=0; i<n; i++){
        board[i] = []; // <-- this is missing!
        for(var j=0; j<n; j++){
            board[i][j]=0;
        }
    }
    return board;
}
document.write('<pre>' + JSON.stringify(makeBoard(5), 0, 4) + '</pre>');

Another version without for loop

function makeBoard(n){
    return Array.apply(null, {length: n}).map(function () {
        return Array.apply(null, {length: n}).map(function () {
            return 0;
        });
    });
}
document.write('<pre>' + JSON.stringify(makeBoard(5), 0, 4) + '</pre>');

edited Apr 7, 2016 at 19:35

answered Apr 7, 2016 at 19:24

Nina Scholz

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Comments

tjugg · Accepted Answer · 2016-04-07 19:29:38Z

0

You generate an array and then loop new arrays inside of that. Something like this:

var arr = new Array(10);
for (var i = 0; i < 10; i++) {
  arr[i] = new Array(6);
}

answered Apr 7, 2016 at 19:29

tjugg

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