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]]

• user1243746: Thanks to all by the different implementations to solve it.

Answer 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.

Answer 2

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);

Answer 3

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;
}