Module:TableTools

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Revision as of 02:44, 19 December 2013 by >Mr. Stradivarius (add isNan function, shallowClone function and removeDuplicates function, fix up valueIntersection function to work properly for NaNs)
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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 libraryUtil = require('libraryUtil')

local p = {}

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

-- 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 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 p.isPositiveInteger(v)
	if type(v) == 'number' and v >= 1 and floor(v) == v and v < infinity then
		return true
	else
		return false
	end
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 p.isNan(v)
	if type(v) == 'number' and tostring(v) == '-nan' then
		return true
	else
		return false
	end
end

--[[
------------------------------------------------------------------------------------
-- shallowClone
--
-- This returns a clone of 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 p.shallowClone(t)
	local ret = {}
	for k, v in pairs(t) do
		ret[k] = v
	end
	return ret
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 p.removeDuplicates(t)
	local isNan = p.isNan
	local ret, exists = {}, {}
	for i, 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[#ret + 1] = v
		else
			if not exists[v] then
				ret[#ret + 1] = v
				exists[v] = true
			end
		end	
	end
	return ret
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 lim = select('#', ...) 
	if lim == 0 then
		error("no arguments passed to 'union'", 2)
	end
	local ret, trackArrays = {}, {}
	for i = 1, lim do
		local t = select(i, ...)
		checkType('union', i, t, 'table')
		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 lim = select('#', ...) 
	if lim == 0 then
		error("no arguments passed to 'valueUnion'", 2)
	end
	local vals, ret = {}, {}
	for i = 1, lim do
		local t = select(i, ...)
		checkType('valueUnion', i, t, 'table')
		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 lim = select('#', ...) 
	if lim == 0 then
		error("no arguments passed to 'intersection'", 2)
	end
	local ret, track, pairCounts = {}, {}, {}
	for i = 1, lim do
		local t = select(i, ...)
		checkType('intersection', i, t, 'table')
		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 lim = select('#', ...) 
	if lim < 2 then
		error(lim .. ' argument' .. (lim == 1 and '' or 's') .. " passed to 'intersection' (minimum is 2)", 2)
	end
	local isNan = p.isNan
	local vals, ret = {}, {}
	local isSameTable = true -- Tracks table equality.
	local tableTemp -- Used to store the table from the previous loop so that we can check table equality.
	for i = 1, lim do
		local t = select(i, ...)
		checkType('valueIntersection', i, t, 'table')
		if tableTemp and t ~= tableTemp then
			isSameTable = false
		end
		tableTemp = t
		for k, v in pairs(t) do
			-- NaNs are never equal to any other value, so they can't be in the intersection.
			-- Which is lucky, as they also can't be table keys.
			if not isNan(v) then
				local valCount = vals[v] or 0
				vals[v] = valCount + 1
			end
		end
	end
	if isSameTable then
		-- If all the tables are equal, then the intersection is that table (including NaNs).
		-- All we need to do is convert it to an array and remove duplicate values.
		for k, v in pairs(tableTemp) do
			ret[#ret + 1] = v
		end
		return p.removeDuplicates(ret)
	end
	for val, count in pairs(vals) do
		if count == lim then
			ret[#ret + 1] = val
		end
	end
	return ret
end

--[[
------------------------------------------------------------------------------------
-- complement
--
-- This returns the relative complement of t1, t2, ..., in tn. The complement
-- is of key/value pairs. This is equivalent to all the key/value pairs that are in
-- tn but are not in t1, t2, ... tn-1.
------------------------------------------------------------------------------------
--]]
function p.complement(...)
	local lim = select('#', ...) 
	if lim == 0 then
		error("no arguments passed to 'complement' (minimum is two)", 2)
	elseif lim == 1 then
		error("only one argument passed to 'complement' (minimum is two)", 2)
	end
	--[[
	-- Now we know that we have at least two sets.
	-- First, get all the key/value pairs in tn. We can't simply make ret equal to tn,
	-- as that will affect the value of tn for the whole module.
	--]]
	local tn = select(lim, ...)
	checkType('complement', lim, tn, 'table')
	local ret = {}
	for k, v in pairs(tn) do
		ret[k] = v
	end
	-- Remove all the key/value pairs in t1, t2, ..., tn-1.
	for i = 1, lim - 1 do
		local t = select(i, ...)
		checkType('complement', i, t, 'table')
		for k, v in pairs(t) do
			if ret[k] == v then
				ret[k] = nil
			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 p.numKeys(t)
	checkType('numKeys', 1, t, 'table')
	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)
	checkType('affixNums', 1, t, 'table')
	checkType('affixNums', 2, prefix, 'string', true)
	checkType('affixNums', 3, suffix, 'string', true)
	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)
	checkType('compressSparseArray', 1, t, 'table')
	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)
	checkType('sparseIpairs', 1, t, 'table')
	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

--[[
------------------------------------------------------------------------------------
-- 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 p.size(t)
	checkType('size', 1, t, 'table')
	local i = 0
	for k in pairs(t) do
		i = i + 1
	end
	return i
end

return p
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