Lua insert multiple variables into a table

Question

My question is how (or if) you can insert two values into a lua table.

I got a function that returns (a variable number of values)

function a(x, y)
   return x, y
end

and another function that inserts that points into a table,

function b(x, y)
   table.insert(myTable, x, y)
end

So how can i make, that i can call function b with a variable number of arguments and insert them all into my table?

As currently written, function b inserts the value y at position x. Is that your intent? If you want to insert multiple values into a table, you have to call table.insert multiple times. This page describes how to handle a variable number of arguments to a function; does that help? — Miles
– Miles, Commented Nov 4, 2012 at 0:47

Luatic · Accepted Answer · 2023-10-02 11:22:18Z

2

The select function operates on the vararg ...

function b(...)
  for i = 1, select('#',...) do
    myTable[#myTable+1] = select(i,...)
  end
end

This will ignore nils in .... myTable is assumed to be a sequence (no nils between non-nil values; {1, nil, 3} would not be a sequence) for this to insert the values in the correct order.

E.g.,

> myTable = {'a','b'}
> b('c','d')
> for i = 1, #myTable do print(myTable[i]) end
a
b
c
d
>

edited Oct 2, 2023 at 11:22

Luatic

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answered Nov 4, 2012 at 1:14

Doug Currie

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2 Comments

Ryan Over a year ago

As a slightly remark, calling b(1,2,nil,4) produces the table {[1] = 1, [2] = 2, [3] = 4}. It can be good, or bad, depending on the requirements.

Luatic Over a year ago

A funny theoretical edge case: If myTable has holes (is not a proper sequence), b may fill them in any order ;)

Ryan · Accepted Answer · 2012-11-04 01:04:14Z

1

If the last parameter for your function is ... (called a vararg function), the Lua interpreter will place any extra arguments into .... You can convert it to a table using {...} and copy the keys/values into your global table named myTable. Here's what your function would look like:

function b(...)
  for k, v in pairs({...}) do
    myTable[k] = v
  end
end

b(1, 2) -- {[1] = 1, [2] = 2} is added to myTable

You should tweak the function depending on whether you want to replace, merge or append elements into myTable.

answered Nov 4, 2012 at 1:04

Ryan

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Comments

darkfrei · Accepted Answer · 2023-10-17 16:07:50Z

1

function tableMultiInsert (list, ...)
  for i, v in ipairs({...}) do
    list[#list+1] = v
  end
end

local list = {}
tableMultiInsert (list, 'a', 'b')
print (table.concat (list, ',')) -- a, b
tableMultiInsert (list, 'c', 'd')
print (table.concat (list, ',')) -- a,b,c,d

edited Oct 17, 2023 at 16:07

answered Oct 2, 2023 at 9:18

darkfrei

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2 Comments

Luatic Over a year ago

Downvoted. Overriding table.insert like this will massively break existing code that uses the index parameter. Small side note: This doesn't deal with nils in ... properly; it will stop at the first nil (it should ideally either ignore nils, or throw an error).

darkfrei Over a year ago

Thanks, you are right! Fixed the code as new function instead of table.insert.

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