# Difference between revisions of "Module:TableTools"

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

```-- This module includes a number of functions that can be useful when dealing with Lua tables.

local p = {}

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

--[[
-----------------------------------------------------------------------------------
-- 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 the 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

--[[
-----------------------------------------------------------------------------------
-- getNumKeys
--
-- 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.getNumKeys(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

--[[
-----------------------------------------------------------------------------------
-- getAffixNums
--
-- 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", getAffixNums will
-- return {1, 3, 6}.
-----------------------------------------------------------------------------------
--]]
function p.getAffixNums(t, prefix, suffix)
prefix = prefix or ''
suffix = suffix or ''
local nums = {}
for k, v in pairs(t) do
if type(k) == 'string' then
local num = mw.ustring.match(k, '^' .. prefix .. '([1-9]%d*)' .. suffix .. '\$')
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.getNumKeys(t)
table.sort(nums)
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.getNumKeys(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
```