JS flat object as matrix coords : how to init all values?

Question

Here is my code :

class ArrayND {
    /**
     * @param {Array<number>} ranks
     */
    constructor (ranks) {
        this.coords = {}
        this._ranks = ranks
    }

    /**
     * @param {number|string} defaultValue
     */
    init (defaultValue) {
        // How to init this.coords with defaultValue given this._ranks ?
    }
}

What i want to achieve :

const myArrayND = new ArrayND([3, 2])
myArrayND.init(5)
/*
myArrayND.coords should be :
{
    0,0: 5,
    0,1: 5,
    1,0: 5,
    1,1: 5,
    2,0: 5,
    2,1: 5
}
*/
myArrayND.coords[[2, 1]] // returns 5

My question is : How to implement the init() function, when the ArrayND can be built with any ranks ?

example :

const firstArray = new ArrayND([])
firstArray.init(5)
// firstArray.coords contains {}

const secondArray = new ArrayND([5])
secondArray.init('aze')
/* secondArray.coords contains {
    0: 'aze',
    1: 'aze',
    2: 'aze',
    3: 'aze',
    4: 'aze',
} */
const thirdArray = new ArrayND([2, 3])
thirdArray.init(2)
/* thirdArray.coords contains {
    0,0: 2,
    0,1: 2,
    0,2: 2,
    1,0: 2,
    1,1: 2,
    1,2: 2,
} */
const anotherExample = new ArrayND([1, 2, 3])
anotherExample.init(1)
/* anotherExample.coords contains {
    0,0,0: 1,
    0,0,1: 1,
    0,0,2: 1,
    0,1,0: 1,
    0,1,1: 1,
    0,1,2: 1,
} */
...

I don't want myObject.coords to contain a multi-dimensional Array because I had other issues to access and set values in a multi-dimensional Array : see JS multidimentional array modify value. It works pretty well, but the ugly switch case is very repelling.

Instead of having

multiDimArray = [
    [
        [1],
        [2],
        [3]
    ],
    [
        [4],
        [5],
        [6]
    ]
]
multiDimArray[0][1][2] // returns 6

Problem is access :

function setValue(indexArray, value) {
    switch (indexArray.length) {
        case 0:
           multiDimArray = value
        case 1:
           multiDimArray[indexArray[0]] = value
        case 2:
           multiDimArray[indexArray[0]][indexArray[1]] = value
        case 3:
           multiDimArray[indexArray[0]][indexArray[1]][indexArrat[2]] =value
        ...
        // Very ugly and isn't truly dynamic
    }
}

I want

multiDimArray = {
    0,0,0: 1,
    0,0,1: 2,
    0,0,2: 3,
    0,1,0: 4,
    0,1,1: 5,
    0,1,2: 6,   
}
multiDimArray[[0, 1, 2]] // returns 6

That way i can access and set the values dynamically with a function like that : (which was done with an ugly switch case in the case of the Array of Arrays)

function setValue(indexArray, value) {
    multiDimArray[indexArray] = value
    // much better than before.
}

So i know the name 'ArrayND' can be a bit misleading, but it's not actually an Array, it's a flat object containing the coordinates of the n-dimensional Array.

Answer 1

If i have understood correctly you can always generate your N dimension array and initialize it as the following. The last parameter is the initialization value. and the previous is the dimensions array where the length of it is the number of dimensions and the items are sizes of each dimension of the array to be created.

To instantiate multi dimensional array we have to have an Array.prototype.clone() method at hand in order to prevent references to get copied. So it goes like this.

Object.prototype.getNestedValue = function(...a) {
  return a.length > 1 ? (this[a[0]] !== void 0 && this[a[0]].getNestedValue(...a.slice(1))) : this[a[0]];
};

Array.prototype.clone = function(){
  return this.reduce((p,c,i) => (p[i] = Array.isArray(c) ? c.clone() : c, p),[])
}

function arrayND(...n){
  return n.reduceRight((p,c) => c = (new Array(c)).fill(true).map(e => Array.isArray(p) ? p.clone() : p ));
}


var m = arrayND(...[3,4,2,3],5);
m[0][2][1][2] = "five";

console.log(JSON.stringify(m,null,2));

console.log(m.getNestedValue(2,3,1,2));

You can of course do the same with Array.prototype.reduce() but i prefer right to left for the sake of abstraction

Answer 2

If you want to fill your custom object with defaultValue for each 'x,y' attributes, and retrieve the value with [x, y], you can do:

init ( defaultValue ) {
    for ( var x = 0; x < this._ranks[ 0 ]; x += 1 ) {
        for ( var y = 0; y < this._ranks[ 1 ]; y += 1 ) {
            this.coords[ String( x ) + ',' + String( y ) ] = defaultValue;
        }
    }
}

and use a getter like:

get valueAt( _coords ) {
    return this.coords[ _coords.join( ',' ) ];
}