How to access a table using a string in Lua

Question

I am trying to remove mainMenuButtonGroup1 through mainMenuButtonGroup6.

To do this I think I need to do the following: [mainMenuButtonGroup..n] How would I do that?

local mainMenuButtonGroup1 = { 1,2 }
local mainMenuButtonGroup2 = { 3,4 }
local mainMenuButtonGroup3 = { 5,6 }
local mainMenuButtonGroup4 = { 7,8 }
local mainMenuButtonGroup5 = { 9,10 }
local mainMenuButtonGroup6 = { 11,12 }

for n = 1, 6 do
      [mainMenuButtonGroup..n] = nil
end

This is a table of display objects in the Corona SDK. In any case, _G would work, I think, if these where global but they are not :( — Gullie667
– Gullie667, Commented Nov 22, 2013 at 16:57
Do you need help iterating a table then? Or local variables? — Ryan Stein
– Ryan Stein, Commented Nov 22, 2013 at 17:00
I need help understanding how to concatenate 2 strings and then use that string to refer to a local table variable. I will then be doing "things" to said table variable. Basically, I don't want to repeat my code 6 times. — Gullie667
– Gullie667, Commented Nov 22, 2013 at 17:22
Why do you want to do '"things" to [a] variable'? Is it captured in a closure? Your code doesn't show that; And note that variables don't have types in Lua. If you want to do things to a table value, that is a different question. Your code doesn't show that either. — Tom Blodget
– Tom Blodget, Commented Nov 24, 2013 at 5:23

Ryan Stein · Accepted Answer · 2013-11-22 18:04:35Z

2

Based on your comments, I assume this is something like what you want to do, where t is the table that you mentioned.

for i = 1, 6 do
    local k = 'mainMenuButtonGroup' .. i
    t[k]:removeSelf()
    t[k] = nil
end

String concatenation is performed by the .. double period operator, and table indexing via . or []. In this case, you're indexing via [] because you're using a variable and not a constant name.

Edit: Put your similar local variables into a table instead. It makes it far, far easier to iterate as a group. In fact, the only way I know of to iterate locals is through the debug library.

local mainMenuButtonGroup = { {1,2}, {3,4}, {5,6}, {7,8}, {9,10} }
table.insert(mainMenuButtonGroup, {11,12})

for i = 1, 6 do
    mainMenuButtonGroup[i] = nil
end

Note, however, that setting a numeric index in a table to nil does not rearrange the table's numerically indexed values. I.e., you'll leave the table with holes. See table.remove.

edited Nov 22, 2013 at 18:04

answered Nov 22, 2013 at 17:29

Ryan Stein

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3 Comments

Gullie667 Over a year ago

In your example k the the table I want to edit. I altered my question's code for clarity.

Ryan Stein Over a year ago

@Gullie667 I've edited my answer in response. Please let me know what you think.

Gullie667 Over a year ago

Thanks for the answer. I guess doing it the way I originally wanted to isn't possible in LUA. I'd plus ya up but lack the rep. Thanks though.

John Zwinck · Accepted Answer · 2013-11-23 01:45:55Z

1

Assuming the variables are global, they will be in the _G table:

for n = 1, 6 do
   for i = _G['mainMenuButtonGroup'..n].numChildren, 1, -1 do
      _G['mainMenuButtonGroup'..n][i]:removeSelf()
      _G['mainMenuButtonGroup'..n][i] = nil
   end
end

If they are local, you can use debug.getlocal, but you will have to loop over all the locals until you find the names you want. Not ideal, but possible.

edited Nov 23, 2013 at 1:45

answered Nov 22, 2013 at 15:45

John Zwinck

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1 Comment

Gullie667 Over a year ago

These variables are not global. :(

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