Check value in array at specific index?

Question

I'm having a bit of trouble with something....

Basicly I have this array (2 dimensional) that stores tiles (basic div's with colors etc...), one may change the properties of a specific tile by doing;

world[x][y].style blabla somehting

Now, I'm starting to do a bit of pathfinding to be able to walk around on these tiles, lets say I have a 10x10 grid of tiles, ranging from -5,-5 to 5,5 (in coordinates).

I'm sitting on the -5,-5 tile and I click somewhere to "start the pathfinding", my pathfinding thing basicly just finds the 8 adjacent tiles and returns them, then I select the one that brings me closer and I do that X amount of times till I hit my target.

This is no problem if I stand in the middle (0,0) and try to go somewhere, but since I'm in the corner of my "world" I get a few problems when searching for the adjacent tiles;

--# o o o o--

--o o o o o--

Lets say this is my world, # being the character, o being empty tiles and - just being an empty abyss (places where I can't be)

Now I want to go to X;

--# o o o o--

--o o o o o--

--o o X o o--

--o o o o o--

So I start my little pathfinding algorithm but when it searches for adjacent tiles from where I am, it returns an error since there is no tiles left, left+down, left+up, or up (from my position.

--# + o o o--

--+ + o o o--

--o o o o o--

(+) is the tiles that are available but it tries to search for more tiles around me, which results in an error.

I've tried to disclude tiles that doesn't exist by using;

if (world[x][y] !== null) {}
if (world[x][y] != null) {}
if (world[x][y] !== 'undefined') {}
if (world[x][y] != 'undefined') {}
if (!world[x][y]) {}

But then the error is given at the if statement instead of the actuall "tile returning"...

So, how do I precheck if there's something in the array at a specific index (or 2 specific indexe's)?

Also please note that my array does have some gaps, since my world is not only walkable tiles.

if (typeof world[x][y] != 'undefined') {}

john Smith
– john Smith

2013-12-30 00:10:19 +00:00
Commented Dec 30, 2013 at 0:10 — john Smith
– john Smith, Commented Dec 30, 2013 at 0:10

vivekvasani · Accepted Answer · 2013-12-30 00:16:05Z

2

You need to validate the row/column at world[x] before checking world[x][y]

if (!world[x] || !world[x][y]) {
    // Tile does not exist
}else{
    // Tile exists
}

answered Dec 30, 2013 at 0:16

vivekvasani

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Josh Beam · Accepted Answer · 2013-12-30 00:17:00Z

0

If you type this line in to your console all by itself:

console.log(typeof x); //output: undefined

without ever having defined any element named 'x', the statement will evaluate to 'undefined'.

Potentially then you can use typeof in your if...else statements to check for an undefined type (which would be the type of something that doesn't exist yet.)

answered Dec 30, 2013 at 0:17

Josh Beam

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Mattias Åslund · Accepted Answer · 2013-12-30 00:27:48Z

0

One effective way of solving this problem is to make the world one "ring" wider (12x12 instead of 10x10) with empty-abyss tokens in all outer tiles. Now the character will never test undefined tiles and your algo will work.

answered Dec 30, 2013 at 0:27

Mattias Åslund

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user1938578 · Accepted Answer · 2013-12-30 00:58:55Z

0

I would suggest that you check the indices (x and y) before asking for the "tile". If you can afford requiring a tile to be returned a little algorithm checking whether what directions can have a tile to be returned seems not very hard.

As a suggestion, you could write a function that returns the actual "neighboring/adjacent" tiles _using_the_index_values_, taking into account that there are no tiles "left" of -5 or "right of +5, etc.

That would mean that not all "neighboring tiles" arrays will have the same amount of tiles, but you can easily manipulate, traverse, know the length (of) etc and array.

If I had more details of the "pathfinding algorithm" I might be able to write sample code. (Hope it helps.)

edited Dec 30, 2013 at 0:58

answered Dec 30, 2013 at 0:28

user1938578

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