Lua table functions

Lua table functions

These are the functions in the "table" table.

Tables are collections of key/value pairs, where both the key and the value can be any Lua data type, except nil.

Tables are indexed by the key, so if you know the key you can quickly retrieve the value. If you don't know the keys you can search the table using the "pairs" or "ipairs" functions.

Since keys and values can be any data type (except nil) it follows that tables can contain other tables.

A table's size (which is only relevant for numerically-indexed tables) is one less than the first integer index with a nil value. If the table has "holes" in it - that is, numeric keys with gaps in the sequence - then the table size is not guaranteed to be the the last gap. Lua does a binary search to try to find a gap, it does not necessarily find the first or last one.

If you are planning to treat your tables as vectors (that is, with numeric keys and a size) then we recommend that you do not allow gaps in the sequence.

If you want to know if a table is empty, or not, you can test:

if next (t) == nil then
  -- table t is empty
end -- if empty

The behaviour of tables can be modified somewhat by attaching a "metatable" to them with the setmetatable function.