Is it possible to define and initialize multidimensional arrays in JavaScript in one line of code?

Question

Sorry if this is too basic, but I am struggling at defining 4-dimensional array (of size 6x6x6x6) in JavaScript and initializing it to all 1's. What's the easiest way to do this?

Thanks!

possible duplicate of [JavaScript Multidimensional Arrays](http://stackoverflow.com/questions/2808926/javascript-multidimensional-arrays) — Frankie, Jun 07 '12 at 23:45
Javascript does not have multidimensional arrays but rather arrays of arrays. — Frankie, Jun 07 '12 at 23:45
@ddlshack: 4-dimensional array with size of each dimension = 6, obviously. `[[[[1]]]]` <--- this is example of `1x1x1x1` — zerkms, Jun 07 '12 at 23:52
@ddlshack well not really; a multi-dimensional array in a language like C or FORTRAN has fixed values for each dimension and is stored in a contiguous block of memory. — Pointy, Jun 07 '12 at 23:55
On a side-note, how would you generalise the creation of an n-dimensional AxBxCxDx... matrix? — Cameron Martin, Jun 08 '12 at 00:05
@ddlshack, there is a slight difference... and John has put it very elegantly here http://stackoverflow.com/a/597790/67945 — Frankie, Jun 08 '12 at 00:08

Elias Zamaria · Answer 1 · 2012-06-08T00:08:20.227

3

You can use the literal syntax, but it would be very big and cumbersome. You may want to try something like this:

var x = [1, 1, 1, 1, 1, 1];
for (var i = 1; i < 4; i++) {
    x = [x, x, x, x, x, x];
}

I found a slightly simpler solution:

var x = 1;
for (var i = 0; i < 4; i++) {
    x = [x, x, x, x, x, x];
}

edited Jun 08 '12 at 00:08

answered Jun 07 '12 at 23:58

Elias Zamaria

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thanks! btw, this question wasn't a challenge, i needed this for a combinatorics-related problem and you saved my day :) funny that defining an array could be so unintuitive... – Ognjen Jun 08 '12 at 00:09

Cameron Martin · Answer 2 · 2012-06-08T00:28:01.840

Seems like there should be easier way, but this will do it.

var array = [];

for(var i=0; i<6; i++) {
    for(var j=0; j<6; j++) {
        for(var k=0; k<6; k++) {
            for(var l=0; l<6; l++) {
                array[i][j][k][l]=1;
            }
        }
    }
}

Edit

To generate an n-dimensional AxBxCxDx... array (untested):

Array.prototype.fill = function(elem, n) {
    for(var i=0; i<n; i++, this.push(elem));
}

function generateArray() {
    var dimensions = Array.prototype.slice.call(arguments);

    var x = 1;
    for (var i = dimensions.length-1; i >= 0; i--) {
        x = [].fill(x, dimensions[i]);
    }
    return x;
}

to generate a 2x3x4x5 matrix:

generateArray(2,3,4,5);

mikez302's solution is better. However, this will allow you to create an AxBxCxD matrix. — Cameron Martin, Jun 08 '12 at 00:03

score 0 · Answer 3 · answered May 14 '13 at 16:22

I implemented ddlshack's generalized method, but ran into an issue due to the fact that arrays are "pass by reference" in JavaScript. This resulted in each dimension of the array holding multiple references to the same array rather than copies of it. To correct the issue, I implemented the solution as follows (the only other difference being that I used a second function rather than modify Array's prototype).

var fillArray = function(val, dim) {
    var a = [];
    for (var i = 0; i < dim; i++) {
        if (Object.prototype.toString.call(val) === "[object Array]") {
            val = val.slice(0);
        }

        a.push(val);
    }

        return a;
};

var generateArray = function() {
    var dimensions = Array.prototype.slice.call(arguments),
        val = 0;

    for (var i = (dimensions.length - 1); i >= 0; i--) {
        val = fillArray(val, dimensions[i]);
    }

    return val;
};

Is it possible to define and initialize multidimensional arrays in JavaScript in one line of code?

3 Answers3