How to get number of entries in a Lua table

Question

Sounds like a  let me google it for you  question  but somehow I can t find an answer  The Lua   operator only counts entries with integer keys  and so does table getn   tbl      tbl  test     47 tbl 1    48 print  tbl  table getn tbl     -- prints  1     1   count   0 for   in pairs tbl  do count   count   1 end print count             -- prints  2    How do I get the number of all entries without counting them

User · Answer

You can set up a meta-table to track the number of entries  this may be faster than iteration if this information is a needed frequently

User · Answer

You could use penlight library  This has a function size which gives the actual size of the table   It has implemented many of the function that we may need while programming and missing in Lua   Here is the sample for using it    gt  tablex   require  pl tablex   gt  a       gt  a 2    2  gt  a 3    3   gt  a  blah     24   gt   a 0   gt  tablex size a  3

User · Answer

I stumbled upon this thread and want to post another option  I m using Luad generated from a block controller  but it essentially works by checking values in the table  then incrementing which value is being checked by 1  Eventually  the table will run out  and the value at that index will be Nil  So subtract 1 from the index that returned a nil  and that s the size of the table  I have a global Variable for TableSize that is set to the result of this count  function Check Table Size     local Count   1   local CurrentVal    CueNames tonumber Count      local repeating   true   print Count    while repeating    true do     if CurrentVal    nil then       Count   Count   1       CurrentVal   CueNames tonumber Count        else       repeating   false       TableSize   Count - 1     end   end   print TableSize  end

User · Answer

You already have the solution in the question -- the only way is to iterate the whole table with pairs       function tablelength T    local count   0   for   in pairs T  do count   count   1 end   return count end   Also  notice that the     operator s definition is a bit more complicated than that  Let me illustrate that by taking this table   t    1 2 3  t 5    1 t 9    1   According to the manual  any of 3  5 and 9 are valid results for  t  The only sane way to use it is with arrays of one contiguous part without nil values

User · Answer

function GetTableLng tbl    local getN   0   for n in pairs tbl  do      getN   getN   1    end   return getN end  You re right  There are no other way to get length of table

User · Answer

local function CountedTable x      assert type x      table    bad parameter  1  must be table        local new t          local mt           --  all  will represent the number of both     local all   0     for k  v in pairs x  do         all   all   1     end      mt   newindex   function t  k  v          if v    nil then             if rawget x  k     nil then                 all   all - 1             end         else             if rawget x  k     nil then                 all   all   1             end         end          rawset x  k  v      end      mt   index   function t  k          if k     totalCount  then return all         else return rawget x  k  end     end      return setmetatable new t  mt  end  local bar   CountedTable   x   23  y   43  z   334   true    true    assert bar totalCount    4  assert bar x    23  bar x   nil assert bar totalCount    3  bar x   nil assert bar totalCount    3  bar x   24 bar x   25 assert bar x    25  assert bar totalCount    4

User · Answer

seems when the elements of the table is added by insert method  getn will return correctly  Otherwise  we have to count all elements  mytable      element1    version   1 1  element2    version   1 2  table insert mytable  element1  table insert mytable  element2  print table getn mytable     It will print 2 correctly

User · Answer

There s one way  but it might be disappointing  use an additional variable  or one of the table s field  for storing the count  and increase it every time you make an insertion   count   0 tbl       tbl  test     47 count   count   1  tbl 1    48 count   count   1  print count    -- prints  2    There s no other way  the   operator will only work on array-like tables with consecutive keys

User · Answer

The easiest way that I know of to get the number of entries in a table is with       tableName gets the number of entries as long as they are numbered   tbl        1       2       3       4       5    print  tbl --prints the highest number in the table  5   Sadly  if they are not numbered  it won t work

[lua] How to get number of entries in a Lua table?

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