Question

I have several tables/variables (sampled below):

mytable = { ['100'] = { ['2']=0,['3']=0,['5']=0,['6']=0,['7']=0,['9']=0},
            ['101'] = { ['8']={['81']=0,['86']=0},
                        ['13']={['81']=0},
                        ['30']={['81']=0,['82']=0,['83']=0,['84']=0,['85']=0} },
            ['102'] = { ['81']={['location']='left',['3']=1} }
          }
mytable2 = 5

I need a function to pass a table/variable structured like one of the two above (could be either one) that will differentiate between current and previous data, and return a table/variable that only consists of the data that has changed since last called per client (a unique ID passed with the table/variable). The tables can grow or change between execution of the function.

So if the following updates occurred between execution of the function:

mytable['101']['8']['81']=1
mytable['102']['81']['4']=0

the function would return

mytable = { ['101'] = { ['8']={['81']=1} },
            ['102'] = { ['81']={['4']=0} }
          } 

Answer 1

Although this adds empty keys, I think it will work for me:

--t is the table and pt is the previous table

function deepchange(t,pt)
if (pt == nil) then return t, true end
if type(t) ~= 'table' then return t,t ~= pt end
local res = {}
local sd = false
for k,v in pairs(t) do
    if type(v) == 'table' then v = deepchange(v,pt[k]) end
    if pt[k] ~= v then 
        res[k] = v
        sd = true
    end
end
return res,sd
end

UPDATED to handle second case and remove unnecessary lines related to get and set metatable…

UPDATED again to handle null previous tables.