How to iterate through table in Lua

Question

So  I have a table something along these lines   arr       apples      a    red   5      oranges      o    orange   12      pears      p    green   7       It doesn t seem like it s possible to access them based on their index  and the values themselves are tables  so I just made the first value of the nested table the index of it  so it now looks like this   arr       apples     0   a    red   5      oranges     1   o    orange   12      pears     2   p    green   7       So  now any time I use one of these tables  I know what the index is  but still can t get to the table using the index  so I started to write a function that loops through them all  and check the indexes until it finds the right one  Then I realized    how can I loop through them if I can t already refer to them by their index  So  now I m stuck  I really want to be able to type arr apples vs arr 1  most of the time  but of course it s necessary to do both at times

User · Accepted Answer

To iterate over all the key-value pairs in a table you can use pairs:

for k, v in pairs(arr) do
  print(k, v[1], v[2], v[3])
end

outputs:

pears   2   p   green
apples  0   a   red
oranges 1   o   orange

Edit: Note that Lua doesn't guarantee any iteration order for the associative part of the table. If you want to access the items in a specific order, retrieve the keys from arr and sort it. Then access arr through the sorted keys:

local ordered_keys = {}

for k in pairs(arr) do
    table.insert(ordered_keys, k)
end

table.sort(ordered_keys)
for i = 1, #ordered_keys do
    local k, v = ordered_keys[i], arr[ ordered_keys[i] ]
    print(k, v[1], v[2], v[3])
end

outputs:

  apples  a   red     5
  oranges o   orange  12
  pears   p   green   7

User · Answer

For those wondering why ipairs doesn t print all the values of the table all the time  here s why  I would comment this  but I don t have enough good boy points     The function ipairs only works on tables which have an element with the key 1  If there is an element with the key 1  ipairs will try to go as far as it can in a sequential order  1 -  2 -  3 -  4 etc until it cant find an element with a key that is the next in the sequence  The order of the elements does not matter    Tables that do not meet those requirements will not work with ipairs  use pairs instead   Examples   ipairsCompatable     AAA    BBB    CCC   ipairsCompatable2     1     DDD    2     EEE    3     FFF   ipairsCompatable3     3     work    2     does    1     this    notIpairsCompatable     2     this    3     does    4     not   notIpairsCompatable2     2     this    5     doesn t    24     either     ipairs will go as far as it can with it s iterations but won t iterate over any other element in the table    kindofIpairsCompatable     2    2    cool      bro    1    1   3    3   5    5     When printing these tables  these are the outputs  I ve also included pairs outputs for comparison   ipairs   ipairsCompatable 1       AAA 2       BBB 3       CCC  ipairs   ipairsCompatable2 1       DDD 2       EEE 3       FFF  ipairs   ipairsCompatable3 1       this 2       does 3       work  ipairs   notIpairsCompatable  pairs   notIpairsCompatable 2       this 3       does 4       not  ipairs   notIpairsCompatable2  pairs   notIpairsCompatable2 2       this 5       doesnt 24      either  ipairs   kindofIpairsCompatable 1       1 2       2 3       3  pairs   kindofIpairsCompatable 1       1 2       2 3       3 5       5 cool    bro

User · Answer

If you want to refer to a nested table by multiple keys you can just assign them to separate keys  The tables are not duplicated  and still reference the same values   arr      apples     a    red   5   arr apples   apples arr 1    apples   This code block lets you iterate through all the key-value pairs in a table  http   lua-users org wiki TablesTutorial    for k v in pairs t  do  print k v  end

User · Answer

All the answers here suggest to use ipairs but beware  it does not work all the time   t     2    44   4  77   6  88   --This for loop prints the table for key value in next t nil do    print key value   end  --This one does not print the table for key value in ipairs t  do    print key value   end

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