How to subtract each element of a table with another table

Question

Hi guys I'm new to lua and I'm having troubles of calculating every element of a tables but it only give me the last resulting calculation

open = {1,2,3,4,5}
close = {6,1,3,1,10}

It only returns

1 5

where it should be a table of each elements subtracted elements

here's my code I really need your help

o = {1,2,3,4,5}
c = {6,1,3,1,10}
for i = 1, #o do
   if c[i] >= o[i] then
      b = c[i] - o[i]
   else
      b = o[i] - c[i]
   end
   body ={}
        table.insert(body,1,b)
end
for key, value in ipairs(body) do print(key, value) end

And avoid adding to the first index of an table to avoid shifting all entries every time. Unless you want to invert the result, you don't want this anyways. — Luke100000, Oct 14 '22 at 06:20

koyaanisqatsi · Answer 1 · 2022-10-15T16:15:27.850

Like @Piglet in the Comment wrote: 'you need to be very analytic about your work if you want to become a programmer.'

So for that analytic stuff you can use Lua standalone.
Give out what is relevant with print()...

> function walkover(open, close)                                                                                                                                                              
>> local open, close, body = open or {1, 2, 3, 4, 5}, close or {6, 1, 3, 1, 10}, setmetatable({}, {__index = table})                                                                          
>> print(#open .. ' Values in table open: ', body.concat(open, ', '))                                                                                                                         
>> print(#close .. ' Values in table close: ', body.concat(close, ', '))                                                                                                                      
>> print(#body .. ' Values in table body: ', body:concat(', '))                                                                                                                               
>> if #open == #close then for i=1, #open do if close[i] >= open[i] then body:insert(close[i] - open[i]) else body:insert(open[i] - close[i]) end end else error('Tables do not have same leng
th') end                                                                                                                                                                                      
>> print(#body .. ' Values in table body: ', body:concat(', '))                                                                                                                               
>> return body                                                                                                                                                                                
>> end                                                                                                                                                                                        
> walkover()                                                                                                                                                                                  
5 Values in table open:         1, 2, 3, 4, 5                                                                                                                                                 
5 Values in table close:        6, 1, 3, 1, 10                                                                                                                                                
0 Values in table body:                                                                                                                                                                       
5 Values in table body:         5, 1, 0, 3, 5                                                                                                                                                 
table: 0x5661e300                                                                                                                                                                             
> walkover({9,8,7,6,5},{4,3,2,1,0})                                                                                                                                                           
5 Values in table open:         9, 8, 7, 6, 5                                                                                                                                                 
5 Values in table close:        4, 3, 2, 1, 0                                                                                                                                                 
0 Values in table body:                                                                                                                                                                       
5 Values in table body:         5, 5, 5, 5, 5                                                                                                                                                 
table: 0x5661e7f0                                                                                                                                                                             
> walkover({9,8,7,6,5},{4,3,2,1,0,-1})                                                                                                                                                        
5 Values in table open:         9, 8, 7, 6, 5                                                                                                                                                 
6 Values in table close:        4, 3, 2, 1, 0, -1                                                                                                                                             
0 Values in table body:                                                                                                                                                                       
stdin:6: Tables do not have same length                                                                                                                                                       
stack traceback:                                                                                                                                                                              
        [C]: in function 'error'                                                                                                                                                              
        stdin:6: in function 'walkover'                                                                                                                                                       
        (...tail calls...)                                                                                                                                                                    
        [C]: in ?

This Example using the minimal error handling that checks the length of open against close and if equal do the math.

PS: If you dont understand the body constructor: setmetatable({}, {__index = table})
This Constructor adds all table Library function as methods.
This body will also returned with its metamethods.
So this is possible too with walkover()' return value...

print(walkover():concat(', '))

How to subtract each element of a table with another table

1 Answers1