lua: iterate through all pairs in table

Question

I have a sparse lua table and I need to iterate over it. The Problem is, it seems that lua begins the iteration at 1, and terminates as soon as it finds a nil value. Here's and example:

> tab={}
> tab[2]='b'
> tab[5]='e'
> for i,v in ipairs(tab) do print(i,v) end
>               --nothing is output here
> tab[1]='a'
> for i,v in ipairs(tab) do print(i,v) end
1   a
2   b
>               --terminates after 2 (first nil value is tab[3])

Is there any way to get the desired output:

1   a
2   b
5   e

Answer 1

You must use pairs instead of ipairs.

tab={}

tab[1]='a'
tab[2]='b'
tab[5]='e'

for k, v in pairs(tab) do print(k, v) end

Will output (in any order):

1   a
2   b
5   e

ipairs iterates over sequential integer keys, starting at 1 and breaking on the first nil pair.

pairs iterates over all key-value pairs in the table. Note that this is not guaranteed to iterate in a specific order.