Multidimensional array not letting me assign values through loop?

Question

I have a small bit of code that looks like this:

func initAllLabels() {

    var scoreLabels:[[[SKLabelNode]]] = []

    for (var x = 0; x < modesInGame; x++) {
        for (var y = 0; y < levelsInMode; y++) {
            for (z = 0; z < labelsInLevel; z++) {
                scoreLabels[x][y][z] = SKLabelNode(fontNamed: "Font")
            }
        }
    }
}

So what I am trying to do is store all my labels for every game mode. The reason I'm trying to use a multidimensional array is because I will have several labels per level (3-5) and I would like to access them like this:

updateText(scoreLabels[currentMode][currentLevel][thisLabel])

And accessing all the labels for the current label like this:

for label in labelsInLevel:
    label.hidden = false

The problem is that when I try to create all my labels at the start of the game in initAllLabels, I get an "index out of range" error at the first run in the loop (index: 0). I think the problem is because I need to "append" to the array before setting its contents, is this right? How would I accomplish this in an array structure like mine?

Possible duplicate of How to create Swift empty two dimensional array with size — David Gourde
– David Gourde, Commented Dec 11, 2015 at 22:13

Airspeed Velocity · Accepted Answer · 2015-12-12 04:30:48Z

You need to initialize the array to a given size before updating items at positions within it. It might help to start with the single-dimensional case:

var labels: [SKLabelNode] = [] // creates an empty array
// since the array is empty, this will generate an index out of range error:
labels[0] = SKLabelNode(fontNamed: "Font")

Instead you need to extend the array with the elements you want to add. For example,

for _ in 0..<labelsInLevel {
    labels.append(SKLabelNode(fontNamed: "Font"))
}

(the _ means “I don’t care about the actual number of each iteration - normally if you wanted to know this was the ith time around the loop you’d write for i in 0..<n)

There are nicer ways to do this though. But be careful with one of them, the initializer for Array that takes a count and a repeatedValue:

let labels = Array(count: labelsInLevel, repeatedValue: SKLabelNode(fontNamed: "Font”))

SKLabelNode is a reference type. That means that a variable only refers to an instance, and assigning one variable to another only copies the reference. So for example:

let variableOne = SKLabelNode(fontNamed: "Foo")
let variableTwo = variableOne  
// variableTwo now refers to the same instance of SKLabelNode
variableTwo.fontName = "Bar"
print(variableOne) 
// fontName will now be “Bar” even though this was
// done via variableTwo

You get the same effect with the repeatedValue code above. The label is created once, and the same reference to it is inserted multiple times. Change a property on one label in the array, and you change them all. Note the for loop version does not have this problem. Every time around the loop, a new SKLabelNode instance will be created. They won’t be shared.

An alternative to the repeatedValue initializer, that creates without using a for loop is to use map:

(0..<labelsInLevel).map { _ in SKLabelNode(fontNamed: "Font") }

Here, just like in the for loop version, a new SKLabelNode instance is created every time.

(again, we use the _ to indicate we don’t care about the number of the iteration)

Finally, to create the nested multidimensional arrays with the loops inside, you can run map multiple times:

var scoreLabels =
  (0..<modesInGame).map { _ in
    (0..<levelsInMode).map { _ in
      (0..<labelsInLevel).map { _ in
        SKLabelNode(fontNamed: "Font")
      }
    }
  }

Really appreciate the detailed response, had no problems at all with this solution!

David Gourde · Accepted Answer · 2015-12-11 22:38:00Z

-2

You need to initialize the 3D array like this if you want all SKLabelNode to point at different SKLabelNodes :

func initAllLabels() {

    var scoreLabels = [[[SKLabelNode]]](count: modesInGame, repeatedValue:
        [[SKLabelNode]](count: levelsInMode, repeatedValue:
        (0..< labelsInLevel).map { _ in SKLabelNode(fontNamed: "Font") }))
}

The repeatedValue is what you are storing in the cells (type or value) and the count represent the number of times you want to store it in your array.

PS: This answer was tested with Xcode Playground and works perfectly fine.

I edited my answer following Airspeed Velocity's comment.

edited Dec 11, 2015 at 22:38

answered Dec 11, 2015 at 20:42

David Gourde

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1 Comment

Airspeed Velocity Over a year ago

Note, this creates an inner array with every element referring to the same label instance, because SKLabelNode is a reference type. Changing it will change it in every entry. To create an array of different labels, use something like map:

var scoreLabels = Array(count: modesInGame, repeatedValue: Array(count: levelsInMode, repeatedValue: (0..<labelsInLevel).map { _ in SKLabelNode(fontNamed: "Foo") }))

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