Get multidimensional array from function

Question

I'm trying to get a multidimensional array initialized to a value from a function. I've tried it but the result is not what I was expecting.

elemSize is an array with the dimensions, and init is the value for each element.

function MakeArray(elemSize, init) {
    var a = [];

    for (var i = 0; i < elemSize.length; i++) {
        var aj = [];
        for (var j = 0; j < elemSize[i]; j++) {
            aj[j] = init;
        }
        a[i] = aj;
    }

    return a;
}

This is the result

>>> var a = MakeArray([3,2], 5);
undefined
>>> a
[[5, 5, 5], [5, 5]]

but I would get:

[[5 5] [5 5] [5 5]]

Thanks to all by the different implementations to solve it.

user1243746
– user1243746

2012-04-18 23:23:17 +00:00
Commented Apr 18, 2012 at 23:23 — user1243746
– user1243746, Commented Apr 18, 2012 at 23:23

gabitzish · Accepted Answer · 2012-04-18 12:13:37Z

1

You are a little wrong with your logic. Here is the code that outputs what you want (three arrays containing two elements ) :

function MakeArray(elemSize, init) {
    var a = [];

    for (var i = 0; i < elemSize[0]; i++) {
        var aj = [];
        for (var j = 0; j < elemSize[1]; j++) {
            aj[j] = init;
        }
        a[i] = aj;
    }

    return a;
}

First element of elemSize represents the number of arrays, and the second one represents the length of each array.

answered Apr 18, 2012 at 12:13

gabitzish

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Comments

Zeta · Accepted Answer · 2012-04-18 12:19:18Z

Don't iterate over elemSize.length and elemSize[i] but elemSize[0] and elemSize[1]:

function MakeArray(elemSize, init) {
    var a = [];

    for (var i = 0; i < elemSize[0]; i++) {
        var aj = [];
        for (var j = 0; j < elemSize[1]; j++) {
            aj[j] = init;
        }
        a[i] = aj;
    }

    return a;
}

If you want a real multidimensional array, then you have to create a recursive function as your looping approach doesn't work for this:

function MakeArray(elemSize,init){
    if(elemSize.length === 0)
        return init;

    var result = [];
    var otherSize = elemSize.slice(1);
    var otherArray = MakeArray(otherSize,init); 
    for(var i = 0; i < elemSize[0]; ++i){
        result.push(otherArray);
    }
    return result;
}

var myArray = MakeArray([5,5,5],2);

kirilloid · Accepted Answer · 2012-04-18 12:19:09Z

0

You need a recursive algorithm to create arrays with arbitrary amount of dimensions.

function MakeArray(sizes, init) {
    var a = [];
    if (sizes.length > 1) {
        var b = sizes.slice(1);
        for (var i = 0; i < sizes[0]; i++) {
            a.push( MakeArray(b, init) );
        }
    } else {
        for (var i = 0; i < sizes[0]; i++) {
            a.push( init );
        }
    }
    return a;
}

answered Apr 18, 2012 at 12:19

kirilloid

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