Returns an array constructor that produces a table that has a number of functions available as methods: the table library functions, and various vanilla Lua functions and functions from Module:table and Module:fun that operate on arrays or on tables with integer keys.

local Array = require("Module:array")
local nums = Array() -- or Array:new()
nums:type() --> "array"
for i = 1, 5 do
nums:concat(", ") --> "1, 2, 3, 4, 5"

local squares = nums:map(function (num) return num ^ 2 end) -- Returns new array.
squares:concat(', ') --> "1, 4, 9, 16, 25"

local even_squares = squares:filter(function (square) return square % 2 == 0 end)
even_squares:concat(", ") --> "4, 16"

The functions from Module:table and Module:fun are loaded as needed.

Functions from Module:table:

  • compressSparseArray (alias compress), contains, invert, isArray, length, listToSet (alias toSet), maxIndex, numKeys, removeDuplicates, reverse, reverseIpairs, serialCommaJoin, sparseIpairs

Functions from Module:fun. These have a function as the second argument (first argument of method):

  • all, filter, fold, map, some

These functions are included in a funcs subtable of an array (awkward):

  • affixNums, keysToList, numKeys

The following functions return an array (with the array metatable):

  • affixNums, compressSparseArray, keysToList, numKeys, removeDuplicates, reverse

The names with underscores instead of camel case can be used as aliases: for instance, arr:to_set() instead of arr:toSet().

The array constructor behaves differently depending on the arguments supplied to it. Without arguments, it creates an empty table. Given a single table, it adds the metatable to it. If the table has been loaded with mw.loadData, it duplicates the table, removing the metatable that is found in tables loaded with mw.loadData. Otherwise, it creates a new table (array) containing the arguments.

The array constructor does this by adding a metatable. This is similar to how all strings have a metatable that allows the string library functions to be used as methods: for instance, ("abc"):sub(1, 1) for string.sub("abc", 1, 1).

-- author: [[wikt:en:Erutuon]]
-- [[wikt:en:Module:array]] as of 20:42, 27 July 2021. 
-- requires [[Module:table]], [[Module:fun]]

local Array = {}
local array_constructor

-- Copy table library so as not to unexpectedly change the behavior of code that
-- uses it.
local array_methods = mw.clone(table)

-- Create version of table.sort that returns the table.
array_methods.sort = function (t, comp)
	table.sort(t, comp)
	return t

-- ipairs and unpack operate on arrays.
array_methods.ipairs = ipairs
array_methods.unpack = unpack

function array_methods:type()
	local mt = getmetatable(self)
	return type(mt) == "table" and mt.__type or nil

function array_methods:adjustIndex(index)
	index = math.floor(index)
	if index < 0 then
		index = #self + index + 1
	return index

-- string.sub-style slicing.
function array_methods:slice(i, j)
	if i == nil then
		i = 1
	elseif type(i) == "number" then
		i = self:adjust_index(i)
		error("Expected number, got " .. type(i))
	if j == nil or type(j) == "number" then
		j = self:adjust_index(j or -1)
		error("Expected number, got " .. type(j))
	local new_arr = array_constructor()
	local k = 0
	for index = i, j do
		k = k + 1
		new_arr[k] = self[index]
	return new_arr

-- A function to convert string key-table modules such
-- as [[wikt:en:Module:languages/data2]] into arrays.
-- "from" is a bad name.
-- field_for_key supplies the field name in which the
-- key will be stored.
local function to_array(map, field_for_key)
	m_table = m_table or require "Module:table"
	local arr = {}
	local i = 0
	for key, val in pairs(map) do
		i = i + 1
		local new_val = m_table.shallowcopy(val)
		if field_for_key then
			new_val[field_for_key] = key
		arr[i] = new_val
	return array_constructor(arr)

-- Functions from [[Module:table]] that operate on arrays or sparse arrays.
-- List copied from [[Module:table/documentation]].
local operate_on_array = {
	-- non-sparse
	"removeDuplicates", "length", "contains", "serialCommaJoin",
	"reverseIpairs", "reverse", "invert", "listToSet", "isArray",
	-- sparse
	"numKeys", "maxIndex", "compressSparseArray", "sparseIpairs",
	-- tables in general
	"shallowcopy", "deepcopy",

-- Not all of these operate on arrays.
local create_new_array = {
	-- Functions from [[Module:table]] that create an array.
	-- List copied from [[Module:table/documentation]].
	"removeDuplicates", "numKeys", "affixNums", "compressSparseArray",
	"keysToList", "reverse",
	-- Functions from [[Module:table]] that create an table.
	"shallowcopy", "deepcopy",
	-- Functions from [[Module:fun]] that create an array.
	"map", "filter",

-- Functions from [[Module:fun]] that take an array in the second argument.
-- They just have to have the argument order reversed to work as methods of the
-- array object.
local second_argument_is_array = { "map", "some", "all", "filter" }

-- Add aliases for the functions from [[Module:table]] whose names
-- contain "array" or "list", which is redundant, and whose names don't conform
-- to the usual camel case.
-- The key redirects to the value.
local alias_of = {
	compress = "compressSparseArray", keys = "keysToList", toSet = "listToSet",
	deepCopy = "deepcopy", shallowCopy = "shallowcopy",

local function get_module_function(key, module, module_name)
	return module[key] 
		or error("No function named " .. tostring(key) .. " in Module:" .. module_name)

local function wrap_in_array_constructor(func)
	return function (...)
		return array_constructor(func(...))

local function create_array_generating_func(key, module, module_name)
	return wrap_in_array_constructor(get_module_function(key, module, module_name))

local function reverse_arguments(func)
	return function (a, b)
		return func(b, a, true)

local function underscore_to_camel_case(str)
	if type(str) ~= "string" then return str end
	str = str:gsub("_(.)", string.upper)
	return str

local m_table, m_fun
local Array = {}
Array.__type = "array"
function Array:__index(key)
	if type(key) ~= "string" then
		return nil
	-- Convert underscores to camel case: num_keys -> numKeys.
	key = underscore_to_camel_case(key)
	local val = array_methods[key]
	if val then
		return val
	key = alias_of[key] or key
	local func
	m_table = m_table or require "Module:table"
	if m_table.contains(operate_on_array, key) then
		if m_table.contains(create_new_array, key) then
			func = create_array_generating_func(key, m_table, "table")
			func = m_table[key]
	elseif m_table.contains(second_argument_is_array, key) then
		m_fun = m_fun or require "Module:fun"
		local raw_func = reverse_arguments(get_module_function(key, m_fun, "fun"))
		if m_table.contains(create_new_array, key) then
			func = wrap_in_array_constructor(raw_func)
			func = raw_func
	elseif key == "fold" then
		m_fun = m_fun or require "Module:fun"
		local raw_func = get_module_function(key, m_fun, "fun")
		func = function(t, func, accum)
			return raw_func(func, t, accum)
	if func then
		array_methods[key] = func
		return func

function Array.__add(a, b)
	if type(a) == 'table' and type(b) == 'table' then
		m_table = m_table or require "Module:table"
		local new_arr = array_constructor(m_table.shallowcopy(a))
		for _, val in ipairs(b) do
		return new_arr

function Array:new(...)
	local arr
	if select("#", ...) == 1 and type((...)) == "table" then
		arr = ...
		local mt = getmetatable(arr)
		-- If table has been loaded with mw.loadData, copy it to avoid the
		-- limitations of it being a virtual table.
		if mt and mt.mw_loadData then
			m_table = m_table or require "Module:table"
			arr = m_table.shallowcopy(arr)
		arr = { ... }
	return setmetatable(arr, self)

-- Declared as local above.
function array_constructor(...)
	return Array:new(...)

local array_generating_funcs = { from = to_array }
local Array_library_mt = {
	__call =, __index = array_generating_funcs
setmetatable(Array, Array_library_mt)

function Array_library_mt:__index(key)
	key = underscore_to_camel_case(key)
	key = alias_of[key] or key
	if array_generating_funcs[key] then
		return array_generating_funcs[key]
	m_table = m_table or require "Module:table"
	if m_table.contains(create_new_array, key) then
		local func = create_array_generating_func(key, m_table, "table")
		array_generating_funcs[key] = func
		return func

return Array