2D dynamic javascript matrix for coordinates object

Question

I'm trying to make a 2D matrix dynamic system which identifies whether there is an "object" at X,Y coordinates (true), or not (false).

Simplified example code:

var coords = [[]]; // Matrix is over 10,000 x 10,000
var objectX = 76;
var objectY = 54;

coords[objectX][objectY] = true;

//Check to see if there is an object @ coordinates
if(coords[100][65] == false || coords[100][65] === undefined)
{
    //There is no object @ 100 x 65
}
else
{
    //Object detected @ 100 x 65
}

But it seems I can't do it this way, since I think I have to start from [0][0], [0][1], [0][2], ... , ect; or something..

Also, matrix is too large to define via putting it in a loop. I can't have it loading for hours.

I won't mind keeping an array segment 'undefined', as I treat it as false in my code.

How can I accomplish this?

[[]] just creates a nested empty array. You need to create other arrays manually. And then use coords[inLimit1][inLimit2] = Anything; — Tushar
– Tushar, Commented Feb 28, 2016 at 12:55
This is a very weird way for keeping track of things. Is it for display purposes? — Volkan
– Volkan, Commented Feb 28, 2016 at 12:59

trincot · Accepted Answer · 2016-02-28 13:05:35Z

3

You need to make sure the first dimension array exists before you address the second dimension:

if (coords[objectX] === undefined) coords[objectX] = [];
coords[objectX][objectY] = true;

If upfront you know you actually need an element for each X,Y position (which will consume more memory), then initialise the matrix first with a loop:

for (var objectX=0; objectX <= maxX; objectX++) {
    coords[objectX] = [];
    for (var objectY=0; objectY <= maxY; objectY++) {
        coords[objectX][objectY] = false;
    }
}

Depending on your needs, you might get better memory usage and performance if you would use a different structure:

var coords = [];
coords[objectX * (maxX + 1) + objectY] = true;

Or if you do not know the range of X nor Y:

coords = {}; // object whose properties will be X,Y strings:
coords[objectX + ',' + objectY] = true;

edited Feb 28, 2016 at 13:05

answered Feb 28, 2016 at 12:56

trincot

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1 Comment

trincot Over a year ago

You're welcome. I added some alternatives as well, ... they may be of interest.

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