# Module:TableTools

Documentation for this module may be created at Module:TableTools/doc

```--[[
------------------------------------------------------------------------------------
--                               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.                                           --
------------------------------------------------------------------------------------
--]]

local p = {}

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

-- Define a unique value to represent NaN. This is because NaN cannot be used as a table key.
local nan = {}

--[[
------------------------------------------------------------------------------------
-- isPositiveInteger
--
-- This function returns true if the given number 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 p.isPositiveInteger(num)
if type(num) == 'number' and num >= 1 and floor(num) == num and num < infinity then
return true
else
return false
end
end

--[[
------------------------------------------------------------------------------------
-- union
--
-- This returns the union of the key/value pairs of n tables. If any of the tables
-- contain different values for the same table key, the table value is converted
-- to an array holding all of the different values.
------------------------------------------------------------------------------------
--]]
function p.union(...)
local ret, trackArrays = {}, {}
for i = 1, select('#', ...) do
local t = select(i, ...)
for k, v in pairs(t) do
local retKey = ret[k]
if retKey == nil then
ret[k] = v
elseif retKey ~= v then
if trackArrays[k] then
local array = ret[k]
local valExists
for _, arrayVal in ipairs(array) do
if arrayVal == v then
valExists = true
break
end
end
if not valExists then
array[#array + 1] = v
ret[k] = array
end
else
ret[k] = {ret[k], v}
trackArrays[k] = true
end
end
end
end
return ret
end

--[[
------------------------------------------------------------------------------------
-- valueUnion
--
-- This returns the union of the values of n tables, as an array. For example, for
-- the tables {1, 3, 4, 5, foo = 7} and {2, bar = 3, 5, 6}, union will return
-- {1, 2, 3, 4, 5, 6, 7}.
------------------------------------------------------------------------------------
--]]
function p.valueUnion(...)
local vals, ret = {}, {}
for i = 1, select('#', ...) do
local t = select(i, ...)
for k, v in pairs(t) do
if type(v) == 'number' and tostring(v) == '-nan' then
v = nan -- NaN cannot be a table key, so use a proxy variable.
end
vals[v] = true
end
end
for val in pairs(vals) do
if val == nan then
-- This ensures that we output a NaN when we had one as input, although
-- they may have been generated in a completely different way.
val = 0/0
end
ret[#ret + 1] = val
end
return ret
end

--[[
------------------------------------------------------------------------------------
-- intersection
--
-- This returns the intersection of the key/value pairs of n tables. Both the key
-- and the value must match to be included in the resulting table.
------------------------------------------------------------------------------------
--]]
function p.intersection(...)
local ret, track, pairCounts = {}, {}, {}
local lim = select('#', ...)
for i = 1, lim do
local t = select(i, ...)
for k, v in pairs(t) do
local trackVal = track[k]
if trackVal == nil then
track[k] = v
pairCounts[k] = 1
elseif trackVal == v then
pairCounts[k] = pairCounts[k] + 1
end
end
end
for k, v in pairs(track) do
if pairCounts[k] == lim then
ret[k] = v
end
end
return ret
end

--[[
------------------------------------------------------------------------------------
-- valueIntersection
--
-- This returns the intersection of the values of n tables, as an array. For
-- example, for the tables {1, 3, 4, 5, foo = 7} and {2, bar = 3, 5, 6},
-- intersection will return {3, 5}.
------------------------------------------------------------------------------------
--]]
function p.valueIntersection(...)
local vals, ret = {}, {}
local lim = select('#', ...)
for i = 1, lim do
local t = select(i, ...)
for k, v in pairs(t) do
if type(v) == 'number' and tostring(v) == '-nan' then
v = nan -- NaN cannot be a table key, so use a proxy variable.
end
local valCount = vals[v] or 0
vals[v] = valCount + 1
end
end
for val, count in pairs(vals) do
if count == lim then
if val == nan then
-- This ensures that we output a NaN when we had one as input, although
-- they may have been generated in a completely different way.
val = 0/0
end
ret[#ret + 1] = val
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 p.numKeys(t)
local isPositiveInteger = p.isPositiveInteger
local nums = {}
for k, v in pairs(t) do
if isPositiveInteger(k) then
nums[#nums + 1] = k
end
end
table.sort(nums)
return nums
end

--[[
------------------------------------------------------------------------------------
-- affixNums
--
-- This takes a table and returns an array containing the numbers of keys with the
-- specified prefix and suffix. For example, for the table
-- {a1 = 'foo', a3 = 'bar', a6 = 'baz'} and the prefix "a", affixNums will
-- return {1, 3, 6}.
------------------------------------------------------------------------------------
--]]
function p.affixNums(t, prefix, suffix)
prefix = prefix or ''
suffix = suffix or ''
local pattern = '^' .. prefix .. '([1-9]%d*)' .. suffix .. '\$'
local nums = {}
for k, v in pairs(t) do
if type(k) == 'string' then
local num = mw.ustring.match(k, pattern)
if num then
nums[#nums + 1] = tonumber(num)
end
end
end
table.sort(nums)
return nums
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 p.compressSparseArray(t)
local ret = {}
local nums = p.numKeys(t)
for _, num in ipairs(nums) do
ret[#ret + 1] = t[num]
end
return ret
end

--[[
------------------------------------------------------------------------------------
-- sparseIpairs
--
-- This is an iterator for sparse arrays. It can be used like ipairs, but can
-- handle nil values.
------------------------------------------------------------------------------------
--]]
function p.sparseIpairs(t)
local nums = p.numKeys(t)
local i = 0
local lim = #nums
return function ()
i = i + 1
if i <= lim then
local key = nums[i]
return key, t[key]
end
end
end

return p
```