Ruby => Javascript translation

Question

curious... how would you write this Ruby in JS?

Array.new(3, Array.new(3, 0))

which returns

[[0, 0, 0], [0, 0, 0], [0, 0, 0]]

i've tried a variety of things but they all seem messy. i suppose some things just can't be as clean as Ruby, but how would you approach this?

maybe i'll learn a JS trick or two ;)

EDIT It was revealed that this Ruby code does not actually create 3 arrays. It creates 1 array, that the others reference. This was not the intention. I am looking for a way to easily map a 2 dimensional array with X amount of elements, and Y amount of nested elements in JS.

Also... This is a contrived example. the intension is to be able to substitute 3 with any number. this was just an example using 3.

Answer 1

You can define it like so:

var arr = [[0, 0, 0], [0, 0, 0], [0, 0, 0]];

Essentially you're explicitly defining it. However, this array contains references to three different arrays (making a total of 4). To make it behave like ruby, you would need to create a function that mimics this behavior:

function arr(size, element) {
 var ret = [];
 for(var i = 0; i < size; i++) {
 ret.push(element);
 }
 return ret; 
}

Then you could do:

var myArray = arr(3, arr(3, 0)); //myArray contains [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

This is more true to the behavior you see in ruby since each element in the array is a reference to the same array (making a total of just two arrays). You can verify this by doing myArray[0][1] = 2; and then inspecting myArray. You should see the second element in each of the arrays in myArray set to 2.

Answer 2

If you just want an empty array container, just to keep track of the length, or to assign values later on, you can do this, a bit hacky but should work:

var a = [[,,],[,,],[,,]]
a[1][1] = 'foo'
alert(a[1][1]) //foo

Answer 3

The following is valid Javascript syntax, assuming you want to create 4 arrays:

[[0, 0, 0], [0, 0, 0], [0, 0, 0]]

EDIT:

Actually your ruby code only creates TWO arrays. One array is [0,0,0] and the other array contains three references to that array. If you change array[0][2] you also change array[1][2]. Are you sure this is what you want? The equivalent javascript code would be:

var b = [0, 0, 0];
var a = [b, b, b];

• elclanrs: Was about to post this. if compressed [[0,0,0],[0,0,0],[0,0,0]] is around same amount of characters than the ruby version.
• John Riselvato: Oh i like your edit +1, but you'll have to to set b = "[0, 0, 0]";
• David Grayson: John, I'm not sure why you want b to be a string. The OP said nothing about strings. I did just add semicolons though.
• brewster: ah! i did not realize that catch. that was not my intention.

Answer 4

In Ruby you can get the desired effect like this

a = Array.new(3) { Array.new(3, 0) }
p a #[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
a[0][0] = 1
p a #[[1, 0, 0], [0, 0, 0], [0, 0, 0]]

In JS like this

var multi_dim = function(a, b, value) {
 var myObj = [];
 for (i=0;i<a;i++) {
 myObj[i] = [];
 for (j=0;j<b;j++) {
 myObj[i][j] = value;
 }
 }
 return myObj;
};
var c = multi_dim(3,3,0);
WScript.echo(c); //0,0,0,0,0,0,0,0,0
c[0][0]=1
WScript.echo(c); //1,0,0,0,0,0,0,0,0

replace WScript.echo with document.write if not in windows and/or in a browser

Answer 5

I guess you could just do this: http://jsfiddle.net/PZBUr/

var i = "[0, 0, 0]";
var myArray = new Array(i, new Array(i, new Array(i)));
document.write(myArray);
​

• nnnnnn: But that creates nested arrays the first element of each being a string.
• elclanrs: Agree, you'd have to use evil() or mostly find another solution

Answer 6

Another way of doing it is:

var arr = new Array(
 new Array(0, 0, 0),
 new Array(0, 0, 0),
 new Array(0, 0, 0)
);

or simply

var arr = [
 [0, 0, 0],
 [0, 0, 0],
 [0, 0, 0]
]