This first edition was written for Lua 5.0. While still largely relevant for Lua 5.1, there are some differences.
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Part III. The Standard Libraries Chapter 19. The Table Library

19 – The Table Library

The table library comprises auxiliary functions to manipulate tables as arrays. One of its main roles is to give a reasonable meaning for the size of an array in Lua. It also provides functions to insert and remove elements from lists and to sort the elements of an array.