Module:Table

The following documentation is located at Module:Table/documentation. ^[edit]

Useful links: subpage list • transclusions • testcases • sandbox

This module provides functions for dealing with Lua tables. All of them, except for two helper functions, take a table as their first argument.

Some functions are available as methods in the arrays created by Module:array.

Functions by what they do:

• Create a new table:
  • shallowClone, shallowcopy, deepcopy, removeDuplicates, numKeys, affixNums, numData, compressSparseArray, keysToList, reverse, invert, listToSet
• Create an array:
  • removeDuplicates, numKeys, affixNums, compressSparseArray, keysToList, reverse
• Return information about the table:
  • size, length, contains, keyFor, isArray, deepEquals, deepEqualsList
• Treat the table as an array (that is, operate on the values in the array portion of the table: values indexed by consecutive integers starting at 1):
  • removeDuplicates, length, contains, serialCommaJoin, reverseIpairs, reverse, invert, listToSet, isArray, deepEqualsList
• Treat a table as a sparse array (that is, operate on values indexed by non-consecutive integers):
  • numKeys, maxIndex, compressSparseArray, sparseConcat, sparseIpairs
• Generate an iterator:
  • sparseIpairs, sortedPairs, reverseIpairs
• Other:
  • sparseConcat, serialCommaJoin, reverseConcat

The original version was a copy of Module:TableTools on Wikipedia via Module:TableTools on Commons, but new functions have been added since then.

---

--[[
------------------------------------------------------------------------------------
--                      table (formerly TableTools)                               --
--                                                                                --
-- This module includes a number of functions for dealing with Lua tables.        --
-- It is a meta-module, meant to be called from other Lua modules, and should     --
-- not be called directly from #invoke.                                           --
------------------------------------------------------------------------------------
--]]

--[[
	Inserting new values into a table using a local "index" variable, which is
	incremented each time, is faster than using "table.insert(t, x)" or
	"t[#t + 1] = x". See the talk page.
]]

local libraryUtil = require('libraryUtil')

local export = {}

-- Define often-used variables and functions.
local floor = math.floor
local infinity = math.huge
local checkType = libraryUtil.checkType
local checkTypeMulti = libraryUtil.checkTypeMulti

local function _check(funcName, expectType)
	if type(expectType) == "string" then
		return function(argIndex, arg, nilOk)
			checkType(funcName, argIndex, arg, expectType, nilOk)
		end
	else
		return function(argIndex, arg, expectType, nilOk)
			if type(expectType) == "table" then
				checkTypeMulti(funcName, argIndex, arg, expectType, nilOk)
			else
				checkType(funcName, argIndex, arg, expectType, nilOk)
			end
		end
	end
end

--[[
------------------------------------------------------------------------------------
-- isPositiveInteger
--
-- This function returns true if the given value is a positive integer, and false
-- if not. Although it doesn't operate on tables, it is included here as it is
-- useful for determining whether a given table key is in the array part or the
-- hash part of a table.
------------------------------------------------------------------------------------
--]]
function export.isPositiveInteger(v)
	return type(v) == 'number' and v >= 1 and floor(v) == v and v < infinity
end

--[[
------------------------------------------------------------------------------------
-- isNan
--
-- This function returns true if the given number is a NaN value, and false
-- if not. Although it doesn't operate on tables, it is included here as it is
-- useful for determining whether a value can be a valid table key. Lua will
-- generate an error if a NaN is used as a table key.
------------------------------------------------------------------------------------
--]]
function export.isNan(v)
	if type(v) == 'number' and tostring(v) == '-nan' then
		return true
	else
		return false
	end
end

--[[
------------------------------------------------------------------------------------
-- shallowcopy
--
-- This returns a clone of an object. If the object is a table, the value
-- returned is a new table, but all subtables and functions are shared.
-- Metamethods are respected, but the returned table will have no metatable of
-- its own.
------------------------------------------------------------------------------------
--]]
function export.shallowcopy(orig)
	local orig_type = type(orig)
	local copy
	if orig_type == 'table' then
		copy = {}
		for orig_key, orig_value in pairs(orig) do
			copy[orig_key] = orig_value
		end
	else -- number, string, boolean, etc
		copy = orig
	end
	return copy
end

-- An alias for shallowcopy(); prefer shallowcopy().
function export.shallowClone(t)
	return export.shallowcopy(t)
end

------------------------------------------------------------------------------------
-- deepcopy
--
-- Recursive deep copy function. Preserves copied identities of subtables.
-- A more powerful version of mw.clone, as it is able to clone recursive tables without getting into an infinite loop.
-- NOTE: protected metatables will not be copied (i.e. those hidden behind a __metatable metamethod), as they are not accessible by Lua's design. Instead, the output of the __metatable method will be used instead.
-- An exception is made for data loaded via mw.loadData, which has its metatable stripped by default. This is because it has a protected metatable, and the substitute metatable causes behaviour that is generally unwanted. This exception can be overridden by setting `rawCopy` to true.
-- If `noMetatable` is true, then metatables will not be present in the copy at all.
-- If `keepLoadedData` is true, then any data loaded via mw.loadData will not be copied, and the original will be used instead. This is useful in iterative contexts where it is necessary to copy data being destructively modified, because objects loaded via mw.loadData are immutable.
------------------------------------------------------------------------------------

function export.deepcopy(orig, noMetatable, rawCopy, keepLoadedData)
	local already_seen = {}
	
	local function dc(orig, includeMetatable)
		if keepLoadedData then
			local mt = getmetatable(orig)
			if mt and mt.mw_loadData then
				return orig
			end
		end
		if type(orig) == "table" then
			if not already_seen[orig] then
				local copy = {}
				already_seen[orig] = copy
				for key, value in pairs(orig) do
					copy[dc(key, includeMetatable)] = dc(value, includeMetatable)
				end
				if includeMetatable then
					local mt = getmetatable(orig)
					if type(mt) == "table" and (
						(not mt.mw_loadData) or
						(mt.mw_loadData and rawCopy)
					) then 
						setmetatable(copy, dc(mt, includeMetatable))
					end
				end
			end
			return already_seen[orig]
		else
			return orig
		end
	end
	
	return dc(orig, not noMetatable)
end

--[[
------------------------------------------------------------------------------------
-- append
--
-- This appends any number of tables together and returns the result. Compare the Lisp
-- expression (append list1 list2 ...).
------------------------------------------------------------------------------------
--]]
function export.append(...)
	local ret = {}
	for i=1,select('#', ...) do
		local argt = select(i, ...)
		checkType('append', i, argt, 'table')
		for _, v in ipairs(argt) do
			table.insert(ret, v)
		end
	end
	return ret
end

--[[
------------------------------------------------------------------------------------
-- extendList
--
-- Extend an existing list by a new list, modifying the existing list in-place.
-- Compare the Python expression list.extend(new_items). If `insertIfNot` is specified,
-- insertion uses export.insertIfNot() instead of table.insert(), which ensures that
-- duplicate items do not get inserted (at the cost of an M*N operation, where
-- M = #list and N = #new_items).
------------------------------------------------------------------------------------
--]]
function export.extendList(list, new_items, insertIfNOt)
	checkType('extendList', 1, list, 'table')
	checkType('extendList', 2, new_items, 'table')
	for _, item in ipairs(new_items) do
		if insertIfNot then
			export.insertIfNot(list, item)
		else
			table.insert(list, item)
		end
	end
end

--[[
------------------------------------------------------------------------------------
-- removeDuplicates
--
-- This removes duplicate values from an array. Non-positive-integer keys are
-- ignored. The earliest value is kept, and all subsequent duplicate values are
-- removed, but otherwise the array order is unchanged.
------------------------------------------------------------------------------------
--]]
function export.removeDuplicates(t)
	checkType('removeDuplicates', 1, t, 'table')
	local isNan = export.isNan
	local ret, exists = {}, {}
	local index = 1
	for _, v in ipairs(t) do
		if isNan(v) then
			-- NaNs can't be table keys, and they are also unique, so we don't need to check existence.
			ret[index] = v
			index = index + 1
		else
			if not exists[v] then
				ret[index] = v
				index = index + 1
				exists[v] = true
			end
		end
	end
	return ret
end

--[[
------------------------------------------------------------------------------------
-- numKeys
--
-- This takes a table and returns an array containing the numbers of any numerical
-- keys that have non-nil values, sorted in numerical order.
------------------------------------------------------------------------------------
--]]
function export.numKeys(t, checked)
	if not checked then
		checkType('numKeys', 1, t, 'table')
	end
	local isPositiveInteger = export.isPositiveInteger
	local nums = {}
	local index = 1
	for k, _ in pairs(t) do
		if isPositiveInteger(k) then
			nums[index] = k
			index = index + 1
		end
	end
	table.sort(nums)
	return nums
end

function export.maxIndex(t)
	checkType('maxIndex', 1, t, 'table')
	local positiveIntegerKeys = export.numKeys(t)
	if positiveIntegerKeys[1] then
		return math.max(unpack(positiveIntegerKeys))
	else
		return 0 -- ???
	end
end

--[[
------------------------------------------------------------------------------------
-- affixNums
--
-- This takes a table and returns an array containing the numbers of keys with the
-- specified prefix and suffix.
-- affixNums({a1 = 'foo', a3 = 'bar', a6 = 'baz'}, "a")
--		↓
-- {1, 3, 6}.
------------------------------------------------------------------------------------
--]]
function export.affixNums(t, prefix, suffix)
	local check = _check('affixNums')
	check(1, t, 'table')
	check(2, prefix, 'string', true)
	check(3, suffix, 'string', true)
	
	local function cleanPattern(s)
		-- Cleans a pattern so that the magic characters ()%.[]*+-?^$ are interpreted literally.
		s = s:gsub('([%(%)%%%.%[%]%*%+%-%?%^%$])', '%%%1')
		return s
	end
	
	prefix = prefix or ''
	suffix = suffix or ''
	prefix = cleanPattern(prefix)
	suffix = cleanPattern(suffix)
	local pattern = '^' .. prefix .. '([1-9]%d*)' .. suffix .. '$'
	
	local nums = {}
	local index = 1
	for k, _ in pairs(t) do
		if type(k) == 'string' then
			local num = mw.ustring.match(k, pattern)
			if num then
				nums[index] = tonumber(num)
				index = index + 1
			end
		end
	end
	table.sort(nums)
	return nums
end

--[[
------------------------------------------------------------------------------------
-- numData
--
-- Given a table with keys like ("foo1", "bar1", "foo2", "baz2"), returns a table
-- of subtables in the format
-- { [1] = {foo = 'text', bar = 'text'}, [2] = {foo = 'text', baz = 'text'} }
-- Keys that don't end with an integer are stored in a subtable named "other".
-- The compress option compresses the table so that it can be iterated over with
-- ipairs.
------------------------------------------------------------------------------------
--]]
function export.numData(t, compress)
	local check = _check('numData')
	check(1, t, 'table')
	check(2, compress, 'boolean', true)
	
	local ret = {}
	for k, v in pairs(t) do
		local prefix, num = tostring(k):match('^([^0-9]*)([1-9][0-9]*)$')
		if num then
			num = tonumber(num)
			local subtable = ret[num] or {}
			if prefix == '' then
				-- Positional parameters match the blank string; put them at the start of the subtable instead.
				prefix = 1
			end
			subtable[prefix] = v
			ret[num] = subtable
		else
			local subtable = ret.other or {}
			subtable[k] = v
			ret.other = subtable
		end
	end
	if compress then
		local other = ret.other
		ret = export.compressSparseArray(ret)
		ret.other = other
	end
	return ret
end

--[[
------------------------------------------------------------------------------------
-- compressSparseArray
--
-- This takes an array with one or more nil values, and removes the nil values
-- while preserving the order, so that the array can be safely traversed with
-- ipairs.
------------------------------------------------------------------------------------
--]]
function export.compressSparseArray(t)
	checkType('compressSparseArray', 1, t, 'table')
	local ret = {}
	local index = 1
	local nums = export.numKeys(t)
	for _, num in ipairs(nums) do
		ret[index] = t[num]
		index = index + 1
	end
	return ret
end

--[[
------------------------------------------------------------------------------------
-- sparseIpairs
--
-- This is an iterator for sparse arrays. It can be used like ipairs, but can
-- handle nil values.
------------------------------------------------------------------------------------
--]]
function export.sparseIpairs(t)
	checkType('sparseIpairs', 1, t, 'table')
	local nums = export.numKeys(t)
	local i = 0
	return function()
		i = i + 1
		local key = nums[i]
		if key then
			return key, t[key]
		else
			return nil, nil
		end
	end
end

--[[
------------------------------------------------------------------------------------
-- size
--
-- This returns the size of a key/value pair table. It will also work on arrays,
-- but for arrays it is more efficient to use the # operator.
------------------------------------------------------------------------------------
--]]
function export.size(t)
	checkType('size', 1, t, 'table')
	local i = 0
	for _ in pairs(t) do
		i = i + 1
	end
	return i
end

--[[
-- This returns the length of a table, or the first integer key n counting from
-- 1 such that t[n + 1] is nil. It is similar to the operator #, but may return
-- a different value when there are gaps in the array portion of the table.
-- Intended to be used on data loaded with mw.loadData. For other tables, use #.
--]]
function export.length(t)
	local i = 0
	repeat
		i = i + 1
	until t[i] == nil
	return i - 1
end

--[[
Recursively compare two values that may be tables, including tables with
nested tables as values. Return true if both values are structurally equal.
Note that this handles arbitary levels of nesting. If all tables are known
to be lists (with only integral keys), use export.deepEqualsList, which will
be more efficient.

If `includeMetatables` is true, then metatables will also be compared. However,
by default, metatables from mw.loadData will not be included in this comparison.
This is because the metatable changes each time mw.loadData is used, even if
it is used on the same data. This can be overridden by setting `rawCompare` to
true.
]]

function export.deepEquals(x, y, includeMetatables, rawCompare)
	local already_seen = {}
	
	-- This strips metatables only from data loaded via mw.loadData.
	if includeMetatables and not rawCompare then
		x = export.deepcopy(x)
		y = export.deepcopy(y)
	end
	
	local function de(x, y)
		if type(x) == "table" and type(y) == "table" then
			-- Two tables are the same if they have the same number of
			-- elements and all keys that are present in one of the tables 
			-- compare equal to the corresponding keys in the other table, 
			-- using structural comparison.
			-- If an element of x is a table, then its table in `already_seen` 
			-- is checked for y (which means they have been compared before). 
			-- If so, immediately iterate to avoid duplicated work. This avoids 
			-- infinite loops.
			if not already_seen[x] then
				already_seen[x] = {}
				if not already_seen[x][y] then
					already_seen[x][y] = true
					local sizex = 0
					for key, value in pairs(x) do
						if not de(value, y[key]) then
							return false
						end
						sizex = sizex + 1
					end
					if includeMetatables and not de(getmetatable(x), getmetatable(y)) then
						return false
					end
					local sizey = export.size(y)
					if sizex ~= sizey then
						return false
					end
				end
			end
			return true
		end
		return x == y
	end
	
	return de(x, y)
end

--[[
Recursively compare two values that may be lists (i.e. tables with integral
keys), including lists with nested lists as values. Return true if both values
are structurally equal. Note that this handles arbitary levels of nesting.
Results are undefined if tables with non-integral keys are present anywhere in
either structure; if that may be the case, use export.deepEquals, which will
handle such tables correctly but be less efficient on lists than
export.deepEqualsList.
]]
function export.deepEqualsList(x, y)
	local already_seen = {}
	
	local function de(x, y)
		if type(x) == "table" and type(y) == "table" then
			if not already_seen[x] then
				already_seen[x] = {}
				if not already_seen[x][y] then
					already_seen[x][y] = true
					if #x ~= #y then
						return false
					end 
					for key, value in pairs(x) do
						if not de(value, y[key]) then
							return false
						end
					end
				end
			end
			return true
		end
		return x == y
	end
	
	return de(x, y)
end

--[[
Given a list and a value to be found, return true if the value is in the array
portion of the list. Comparison is by value, using `deepEquals`.

NOTE: This used to do shallow comparison by default and accepted a third
'deepCompare' param to do deep comparison. This param is still accepted but now
ignored.
]]
function export.contains(list, x)
	checkType('contains', 1, list, 'table')
	for _, v in ipairs(list) do
		if export.deepEquals(v, x) then return true end
	end
	return false
end

--[[
Given a general table and a value to be found, return true if the value is in
either the array or hashmap portion of the table. Comparison is by value, using
`deepEquals`.

NOTE: This used to do shallow comparison by default and accepted a third
'deepCompare' param to do deep comparison. This param is still accepted but now
ignored.
]]
function export.tableContains(tbl, x)
	checkType('tableContains', 1, tbl, 'table')
	for _, v in pairs(tbl) do
		if export.deepEquals(v, x) then return true end
	end
	return false
end

--[[
Given a list and a value to be inserted, append or insert the value if not
already present in the list. Comparison is by value, using `deepEquals`.
Appends to the end, like the default behavior of table.insert(), unless `pos`
is given, in which case insertion happens at position `pos` (i.e. before the
existing item at position `pos`).

NOTE: The order of `item` and `pos` is reversed in comparison to table.insert(),
which uses `table.insert(list, item)` to insert at the end but
`table.insert(list, pos, item)` to insert at position POS.

NOTE: This used to do shallow comparison by default and accepted a fourth
'deepCompare' param to do deep comparison. This param is still accepted but now
ignored.
]]
function export.insertIfNot(list, item, pos)
	if not export.contains(list, item) then
		if pos then
			table.insert(list, pos, item)
		else
			table.insert(list, item)
		end
	end
end

--[[
	Finds key for specified value in a given table.
	Roughly equivalent to reversing the key-value pairs in the table –
		reversed_table = { [value1] = key1, [value2] = key2, ... }
	– and then returning reversed_table[valueToFind].
	
	The value can only be a string or a number
	(not nil, a boolean, a table, or a function).
	
	Only reliable if there is just one key with the specified value.
	Otherwise, the function returns the first key found,
	and the output is unpredictable.
]]
function export.keyFor(t, valueToFind)
	local check = _check('keyFor')
	check(1, t, 'table')
	check(2, valueToFind, { 'string', 'number' })
	
	for key, value in pairs(t) do
		if value == valueToFind then
			return key
		end
	end
	
	return nil
end

--[[
	The default sorting function used in export.keysToList if no keySort
	is defined.
]]
local function defaultKeySort(key1, key2)
	-- "number" < "string", so numbers will be sorted before strings.
	local type1, type2 = type(key1), type(key2)
	if type1 ~= type2 then
		return type1 < type2
	else
		return key1 < key2
	end
end

--[[
	Returns a list of the keys in a table, sorted using either the default
	table.sort function or a custom keySort function.
	If there are only numerical keys, numKeys is probably more efficient.
]]
function export.keysToList(t, keySort, checked)
	if not checked then
		local check = _check('keysToList')
		check(1, t, 'table')
		check(2, keySort, 'function', true)
	end
	
	local list = {}
	local index = 1
	for key, _ in pairs(t) do
		list[index] = key
		index = index + 1
	end
	
	-- Place numbers before strings, otherwise sort using <.
	if not keySort then
		keySort = defaultKeySort
	end
	
	table.sort(list, keySort)
	
	return list
end

--[[
	Iterates through a table, with the keys sorted using the keysToList function.
	If there are only numerical keys, sparseIpairs is probably more efficient.
]]
function export.sortedPairs(t, keySort)
	local check = _check('keysToList')
	check(1, t, 'table')
	check(2, keySort, 'function', true)
	
	local list = export.keysToList(t, keySort, true)
	
	local i = 0
	return function()
		i = i + 1
		local key = list[i]
		if key ~= nil then
			return key, t[key]
		else
			return nil, nil
		end
	end
end

function export.reverseIpairs(list)
	checkType('reverse_ipairs', 1, list, 'table')
	
	local i = #list + 1
	return function()
		i = i - 1
		if list[i] ~= nil then
			return i, list[i]
		else
			return nil, nil
		end
	end
end

--[[
	A set of functions that, given an array and function, iterate through the array applying that function.
	`reduce` applies func(r, k, v), and returns the result, where r is the value calculated so far, k is an index, and v is the value at index k.  For example, reduce(array, function(a, b) return a + b end) will return the sum of `array`.
	`apply` applies func(k, v), and returns the modified array. For example, apply(array, function(a) return 2*a end) will return an array where each member of `array` has been doubled.
	`all` returns whether func(k, v) is true for all iterations.
	`any` returns whether func(k, v) is true for at least one iteration.
	
	Optional arguments:
		i: start index; negative values count from the end of the array
		j: end index; negative values count from the end of the array
		s: step increment
		These must be non-zero integers.
		The function will determine where to iterate from, whether to iterate forwards or backwards and by how much, based on these inputs (see examples below for default behaviours).
	Examples:
		No values for i, j or s results in forward iteration from the start to the end in steps of 1 (the default).
		s=-1 results in backward iteration from the end to the start in steps of 1.
		i=7, j=3 results in backward iteration from indices 7 to 3 in steps of 1 (i.e. s=-1).
		j=-3 results in forward iteration from the start to the 3rd last index.
		j=-3, s=-1 results in backward iteration from the end to the 3rd last index.
	Note: directionality generally only matters for `reduce`, but values of s > 1 (or s < -1) still affect the return value of `apply`.
]]

local function getIteratorValues(i, j , s, list)
	i = (i and i < 0 and #list - i + 1) or i or (s and s < 0 and #list) or 1
	j = (j and j < 0 and #list - j + 1) or j or (s and s < 0 and 1) or #list
	s = s or (j < i and -1) or 1
	if (
		i == 0 or i % 1 ~= 0 or
		j == 0 or j % 1 ~= 0 or
		s == 0 or s % 1 ~= 0
	) then
		error("Arguments i, j and s must be non-zero integers.")
	end
	return i, j, s
end

function export.reduce(list, func, i, j, s)
	i, j, s = getIteratorValues(i, j , s, list)
	local ret = list[i]
	for k = i + s, j, s do
		ret = func(ret, k, list[k])
	end
	return ret
end

function export.apply(list, func, i, j, s)
	local modified_list = export.deepcopy(list)
	i, j, s = getIteratorValues(i, j , s, modified_list)
	for k = i, j, s do
		modified_list[k] = func(k, modified_list[k])
	end
	return modified_list
end

function export.all(list, func, i, j, s)
	i, j, s = getIteratorValues(i, j , s, list)
	local ret = true
	for k = i, j, s do
		ret = ret and not not (func(k, list[k]))
		if not ret then break end
	end
	return ret
end

function export.any(list, func, i, j, s)
	i, j, s = getIteratorValues(i, j , s, list)
	local ret = false
	for k = i, j, s do
		ret = ret or not not (func(k, list[k]))
		if ret then break end
	end
	return ret
end

--[=[
	Joins an array with serial comma and serial conjunction, normally "and".
	An improvement on mw.text.listToText, which doesn't properly handle serial
	commas.
	
	Options:
		- conj
			Conjunction to use; defaults to "and".
		- italicizeConj
			Italicize conjunction: for [[Module:also]]
		- dontTag
			Don't tag the serial comma and serial "and". For error messages, in
			which HTML cannot be used.
]=]
function export.serialCommaJoin(seq, options)
	local check = _check("serialCommaJoin", "table")
	check(1, seq)
	check(2, options, true)
	
	local length = #seq
	
	if not options then
		options = {}
	end
	
	local conj
	if length > 1 then
		conj = options.conj or "and"
		if options.italicizeConj then
			conj = "''" .. conj .. "''"
		end
	end
	
	if length == 0 then
		return ""
	elseif length == 1 then
		return seq[1] -- nothing to join
	elseif length == 2 then
		return seq[1] .. " " .. conj .. " " .. seq[2]
	else
		local comma = options.dontTag and "," or '<span class="serial-comma">,</span>'
		conj = options.dontTag and ' ' .. conj .. " " or '<span class="serial-and"> ' .. conj .. '</span> '
		return table.concat(seq, ", ", 1, length - 1) ..
				comma .. conj .. seq[length]
	end
end

--[[
	Concatenates all values in the table that are indexed by a number, in order.
	sparseConcat{ a, nil, c, d }  =>  "acd"
	sparseConcat{ nil, b, c, d }  =>  "bcd"
]]
function export.sparseConcat(t, sep, i, j)
	local list = {}
	
	local list_i = 0
	for _, v in export.sparseIpairs(t) do
		list_i = list_i + 1
		list[list_i] = v
	end
	
	return table.concat(list, sep, i, j)
end

--[[
	Values of numberic keys in array portion of table are reversed:
	{ "a", "b", "c" } -> { "c", "b", "a" }
--]]
function export.reverse(t)
	checkType("reverse", 1, t, "table")
	
	local new_t = {}
	local t_len = #t
	local base = t_len + 1
	for i = t_len, 1, -1 do
		new_t[base-i] = t[i]
	end
	return new_t
end

function export.reverseConcat(t, sep, i, j)
	return table.concat(export.reverse(t), sep, i, j)
end

-- { "a", "b", "c" } -> { a = 1, b = 2, c = 3 }
function export.invert(array)
	checkType("invert", 1, array, "table")
	
	local map = {}
	for i, v in ipairs(array) do
		map[v] = i
	end
	
	return map
end

--[[
	{ "a", "b", "c" } -> { ["a"] = true, ["b"] = true, ["c"] = true }
--]]
function export.listToSet(t)
	checkType("listToSet", 1, t, "table")
	
	local set = {}
	for _, item in ipairs(t) do
		set[item] = true
	end
	return set
end

--[[
	Returns true if all keys in the table are consecutive integers starting at 1.
--]]
function export.isArray(t)
	checkType("isArray", 1, t, "table")
	
	local i = 0
	for _ in pairs(t) do
		i = i + 1
		if t[i] == nil then
			return false
		end
	end
	return true
end

--[[
	Add a list of aliases for a given key to a table. The aliases must be given as a table.
--]]

function export.alias(t, k, aliases)
	for _, alias in pairs(aliases) do
		t[alias] = t[k]
	end
end

return export