table.n -- Alternative Table Library for Lua

Lua doesn't have a native array type. Instead it uses the concept of "sequences" (tables containing small consecutive integer keys with non-nil values) to represent arrays. One drawback is that it is difficult to check whether a table is a valid sequence (and neither the length operator # nor the default table library do check), and this may lead to surprising bugs. This module is a drop-in replacement of the default table library that doesn't use sequences or the # operator, but instead requires you to explicitly set and maintain a length field n in your arrays (the functions in this module will update n for you, though).

Extensions

This module additionally contains some useful table-related functions that are not part of the original table standard library.

• table.replace(t1 [, i [, j]], t2 [, m [, n]])

  Replaces the elements with indices i, ..., j in t1 with the elements t2[m], ..., t2[n]. If the two ranges have a different number of indices, the following elements in t1 are shifted to make room or fill the gap, and t1.n is updated accordingly. The default value for i is t1.n+1 (which results in appending to t1), j defaults to t1.n. Default values for m and n are 1 and t2.n, respectively.

• table.zip(f, t1, ...)

  Iterates over all indices from 1 to n (where n is the smallest integer value of the .n fields of all argument tables) and calls the function f with (t1[i], t2[i], etc.) as arguments. All return values of these function calls are appended to a result array that is returned at the end. If f is nil, table.pack is used as a default which results in the usual behavior of the zip function known from other programming languages:

  table.zip( nil, { 1, 2, 3, n=3 }, { "a", "b", "c", n=3 } )
  --> { { 1, "a", n=2 }, { 2, "b", n=2 }, { 3, "c", n=2 }, n=3 }

  However, with a suitable choice of f you can for instance interleave values

  local function id( ... ) return ... end
  table.zip( id, { 1, 2, 3, n=3 }, { "a", "b", "c", n=3 } )
  --> { 1, "a", 2, "b", 3, "c", n=6 }

  or emulate the well-known map or filter functions:

  local function plus3( a ) return a + 3 end
  table.zip( plus3, { 1, 2, 3, n=3 } )
  --> { 4, 5, 6, n=3 }
  local function not_nil( a )
    if a ~= nil then return a end
  end
  table.zip( not_nil, { 1, nil, 2, 3, nil, 4, n=6 } )
  --> { 1, 2, 3, 4, n=4 }

• table.npairs(t [, i]) (or npairs(t [, i]))

  Returns an iterator tuple that, when used in a generic for-loop, iterates over the pairs (1, t[1]), (2, t[2]), ..., until the index reaches t.n. You may specify a starting index different from 1. For convenience and consistency the npairs function is also available in the globals table.

• table.reverse(t [, i [, j]])

  Reverses the elements between indices i and j in table t inplace. i and j default to 1 and t.n, respectively.

• table.rotate(t, m [, i [, j]])

  Shifts the elements between indices i and j in table t m positions to the right. Elements that are shifted beyond j are reinserted at i. m may be negative to rotate in the other direction. Default values for i and j are 1 and t.n, respectively.

• table.shuffle(t [, i [, j]])

  Randomly reorders the elements between indices i and j in table t.

Installation

luarocks install --server=http://luarocks.org/dev table.n

If you want to install manually: Compile the file ltablib.c into a shared library table\n.dll or table/n.so and put it somewhere into your package.cpath.

Contact

Philipp Janda, siffiejoe(a)gmx.net

Comments and feedback are always welcome.

License

table.n is a slightly modified copy of the table library in Lua 5.3 and as such is distributed under the same license (MIT). The full license text follows:

Copyright (C) 1994-2016 Lua.org, PUC-Rio.

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

This module also uses code from the Compat-5.3 project, which is available under the same license (MIT).