Question

I have an object which im converting into an array of coords which will be used to store which coords are “occupied”.

I thought i had it working but on further inspection through console.log the array is missing a fair few results.

So this is basically my object:

var sdata = {"4":{"7":["1","7","3","3"]}};

In words this is:

var sdata = {"X":{"Y":["ID","ID","Width","Height"]}

Ignore ID for this as they are unrelated… but im trying to use this data so that i have the X and Y + the additional X and Y coords related to its tile dimensions width and height.

Imagine if you will the object for 4:7 is 3 by 3 dimensions so resulting in these 9 grid references would exist.

[4:7], [5:7], [6,7]  
[4:8], [5:8], [6,8]  
[4:9], [5:9], [6:9]

So my function to create the coords is :

function populate_collisions() {

  for (var X in sdata) {
    X = parseInt(X);

    for (var Y in sdata[X]) {
      Y = parseInt(Y);
      width = parseInt(sdata[X][Y][2]);
      height = parseInt(sdata[X][Y][3]);

  for (i=X; i!= X+width; i++) {

        if( typeof gcollision[i] == 'undefined' ) {
          gcollision[i] = new Array();
        }
        gcollision[i][Y] = 1

        for (j=Y; j!=Y+height; j++) {

          if( typeof gcollision[X] == 'undefined' ){ 
            gcollision[X] = new Array();
          }
          gcollision[X][j] = 1
        }
      }
    }
  }
}

But my logic must be wrong because im getting this result for my array:

[4] [7] = 1
[4] [8] = 1
[4] [9] = 1
[5] [7] = 1
[6] [7] = 1

Any idea why im missing additional data?

Answer 1

Here’s the fixed code:

function populate_collisions() {

  for (var X in sdata) {
    X = parseInt(X);

    for (var Y in sdata[X]) {
      Y = parseInt(Y);
      var width = parseInt(sdata[X][Y][2]);
      var height = parseInt(sdata[X][Y][3]);

      for (var i=X; i < X+width; i++) {

        if (!gcollision[i]) {
          gcollision[i] = [];
        }
        gcollision[i][Y] = 1;

        for (var j=Y; j < Y+height; j++) {

In the next part, you were using X, which is always 4 so you were just overwriting that array. Use i instead of X.

You don’t need the if test, since the array is created above, unless you really meant gcollision[X][j] or similar. I don’t know as I don’t know the structure you want for the gcollision object.

/*
          if (!gcollision[i][j]) { 
            gcollision[i][j] = [];
          }
*/          
          gcollision[i][j] = 1;
        }
      }
    }
  }
}

For the record, the resulting object (assuming gcollision has no other properties) is:

alert(JSON.stringify(gcollision));
/*
{"4":[null,null,null,null,null,null,null,1,1,1],
 "5":[null,null,null,null,null,null,null,1,1,1],
 "6":[null,null,null,null,null,null,null,1,1,1]}
*/

All those nulls don’t exist, the arrays are sparse, but that’s how JSON represents them.