Using the Array methods with nested (multidimensional) arrays?

Question

I am having problems when using Array methods with nested arrays.

var map = [
        ["Blank", "Blank", "Blank"],
        ["Blank", "Player", "Blank"],
        ["Blank", "Blank", "Blank"]
];

for (i=0; i<map.length; i++) {
        for (j=0; j<map[i].length; j++) {
            var playerY = map[i][j].indexOf("Player");
        }
}

console.log(playerY);

This will always log -1 which is I know an error. Although I think my issue is with using nested arrays. It could also be a problem with the way I am using .indexOf(), or the way I am looping through the arrays. Thank you for helping. Any advise would be appreciated! :)

EDIT: Thank you for all the help. I ended up changing things a lot and not using the .indexOf() method all together. Here is what I ended up doing.

var map = [
        ["Blank", "Blank", "Blank"],
        ["Blank", "Player", "Blank"],
        ["Blank", "Blank", "Blank"]
];

for (x = 0; x < map.length; x++) {
    for (y = 0; y < map[x].length; y++) {
        if (map[x][y] == "Player") {
            console.log("(" + x.toString() + ", " + y.toString() + ")");
        }
    }
}

Every single time through the loop, you update the value of "playerY". After the loop, the value of "playerY" will be what the last iteration set it to. — Pointy
– Pointy, Commented Apr 1, 2013 at 18:07

David G · Accepted Answer · 2013-04-01 18:07:20Z

6

The loop doesn't stop when indexOf finds "Player" inside the nested array. It will continue to loop, thus overwriting the value of playerY with each iteration. To fix this, we must break when indexOf has found the string:

for (i = 0; i < map.length; i++) {
    for (j = 0; j < map[i].length; j++) {
        var playerY = map[i][j].indexOf("Player");

        if (playerY > -1) break; // We have found "Player"
    }
}

answered Apr 1, 2013 at 18:07

David G

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2 Comments

Alpha Centauri A B Over a year ago

Thank you a lot! I wish I could up-vote you but I'm not to 15 yet... I ended up changing things a lot and found that using the .indexOf() method wasn't really necessary. But definitely wouldn't of figured it out the same without with your help. :)

Alpha Centauri A B Over a year ago

yep! :) As you can see I am new... ha

DarkAjax · Accepted Answer · 2013-04-01 18:07:28Z

0

Your problem is that playerY is evaluated for each of map elements, and since the last one doesn't match "Player", your final result is -1.

Basically in this case is as if you were testing this:

var playerY = map[2][2].indexOf("Player");

And since that element is "Blank", it'll return -1

answered Apr 1, 2013 at 18:07

DarkAjax

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1 Comment

Alpha Centauri A B Over a year ago

That makes a lot of sense. Thank you. :)

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