Array within an Array in Lua

Question

If I had code like this in Lua, how would I call 'this'?

array = { this = { pic="hi.png", health=4 } , pos=20 }

Edit:

Say for example I have a table of enemies like:

enemy = {}
enemy[1] = {pic="Ships/enem-01.png", hp=2}
enemy[2] = {pic="Ships/enem-02.png", hp=4}
enemy[3] = {pic="Ships/enem-03.png", hp=3}
enemy[4] = {pic="Ships/enem-04.png", hp=5}
enemy[5] = {pic="Ships/enem-05.png", hp=7}
enemy[6] = {pic="Ships/enem-06.png", hp=9}
enemy[7] = {pic="Ships/enem-07.png", hp=15}

I then want to be able to create a table of there positions.

level1 = {}
level1[1] = { ent = enemy[2], xpos= 20, ypos=20}

how would I call pic, using level1, or wouldn't I?

would I change level1 to be like

level1[1] = {ent = 2, xpos=20, ypos=20}

then use

screen:draw(level[1].xpos, level[1].ypos, enemy[level[1].ent].pic)

I'd call that 'this' a "key" in the table array points to.

jpjacobs
– jpjacobs

2012-01-11 14:03:11 +00:00
Commented Jan 11, 2012 at 14:03 — jpjacobs
– jpjacobs, Commented Jan 11, 2012 at 14:03

borges · Accepted Answer · 2012-01-11 14:16:30Z

3

Remember that there is no such thing as 'array' in Lua. The only existing complex data structure are 'tables', wich are build using { }

Tables are associative structures, where every data stored can be indexed by keys of any type: numbers, strings or even other tables. The only restriction is the nil type.

Let's see an example, we want to build one table with two keys, one number and one string:

example = { [1] = "numberkey", ["key"] = "stringkey" }

Note that in the example above, the table construction is different from your example. You index a table using [ ], like the following example:

example[1]
example["key"]

But this syntax to create and index string keys is quite verbose. So to make our life easier, Lua offers us what it calls a "syntax sugar":

example2 = { [1] = "numberkey", key = "stringkey" }

The contents of this table is the same as before. But the key "key" was declared differently. We can do that with string keys: put them directly in table constructors. And to index them, we can use another "syntax sugar":

example2.key

Back to your example, you can access this, wich is a string key, using:

array.this

Sorry about my english, it is not my first (and second) language.

edited Jan 11, 2012 at 14:16

answered Jan 11, 2012 at 14:06

borges

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1 Comment

jpjacobs Over a year ago

Aside of nil, you can't use NaN as table key either.

kikito · Accepted Answer · 2012-01-11 16:14:54Z

2

Edit:

level1[1] = { ent = enemy[2], xpos= 20, ypos=20}

how would I call pic, using level1, or wouldn't I?

You just need to do this:

level1[1].ent.pic -- "Ships/enem-02.png"

edited Jan 11, 2012 at 16:14

answered Jan 11, 2012 at 13:41

kikito

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