Would this work for updating a table?

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#1

So I am currently playing with tables, and i wanted to see if I could make it have another tables with other keys, get placed into another table that doesn have the same keys, so I can change them accordingly while maintaining their values.

Simply: I’m updating table keys to match another table, as in if one of the table is outdated with missing keys and tables, It would update using the provided table.

Would this work for updating a table?

-- pt = "primary table"
-- ct = "Comparing table"

function update(pt, ct) 
    for i,v in ct do -- iterates through campring table
        if pt[i] == nil then -- if value does not exist
            pt[i] = v -- adds value to table
        end
        if type(v) == "table" then -- if value is a table
            update(v, ct[i]) -- Recusive?
        end
    end

    for i,v in pt do -- iterates through primary table
        if ct[i] == nil then -- if value inside table doesnt exist
            pt[i] = ct[i] -- updates to comparing table value (i think I can just say 'nil' here but idk)
        end
        if type(v) == "table" then -- if value is a table
            update(pt, ct[i]) -- Recursive?
        end
    end

end

So far It appears to be working properly, but I’m not sure if I’m doing it efficiently or If I made any mistakes in it.

Is there anything I can do this?

1 Like
#2

Seems like it would work fine, but it’s not compatible with dictionaries.

#3

I see, but now its giving me the error, attempt to iterate over a nil value, so idk what happened.

#4

This just compares the table to itself.

This updates the root table from the sub table ct[i].

What line does the output say is the problem?

Not sure what is this supposed to be used for. Can you elaborate?

#5

oof.

Line 20, which is this part:

for i,v in ct do

test code:

-- test tables
local t = {
	H = {"hello"};
	Z = {"Hi"};
}
local ct = {
	H = {"hello"};
	I = {"Hi"};
}

print(t, ct) -- prints fine
update(t, ct) -- error line (technically line 20)

print(t)
#6

Since in both loops, you did not check whether or not ct[i] or pt[i] is nil, you’re basically calling update like update(v, nil) whenever ct[i] or pt[i] is actually empty.

From first loop, edit:

if typeof(v) == "table" then -- if value is a table
	if (pt[i] == nil) or not (typeof(pt[i]) == "table") then
		pt[i] = {} -- Overwrite to empty table to allow update to fill all missing details.
	end
	
	update(v, pt[i]) -- Recusive?
end
1 Like
#7

Thanks, but that did not help at all, It still giving me the same error at the same line.

Its happening on the first iteration as in when I first fire the function, and not when the function repeats

#8

Checking if the other table’s index is nil also applies to the second loop.

Not sure if this is how you want it to do:

  1. Check the contents of the comparison table.
  2. Any new index from the comparison table will be inserted to the primary table.
  3. Check the contents of the primary table.
  4. Remove any content from the primary table that does not exist in the comparison table.

This is my revision:

-- test tables
local t = {
	H = {"hello"};
	Z = {"Hi"};
}
local ct = {
	H = {"hello"};
	I = {"Hi"};
}

-- pt = "primary table"
-- ct = "Comparing table"

function deep_clone(t)
	local clone = {}
	
	for index, item in t do
		if typeof(item) == "table" then
			clone[index] = deep_clone(item)
			continue
		end
		
		clone[index] = item
	end
	
	return clone
end

function update(pt, ct) 
	local old_pt = deep_clone(pt)
	
	for i,v in ct do -- iterates through campring table
		warn(i, v)
		if pt[i] == nil then -- if value does not exist
			pt[i] = v -- adds value to table
		end
		if typeof(v) == "table" then -- if value is a table
			if not (typeof(pt[i]) == "table") then
				pt[i] = {} -- Overwrite to empty table to allow update to fill all missing details.
			end
			
			update(pt[i], v) -- Recusive?
		end
	end

	for i,v in old_pt do -- iterates through primary table
		if ct[i] == nil then -- if value inside table doesnt exist
			pt[i] = nil -- simply set to nil
			continue
		end
	end
end

print(t, ct) -- prints fine
update(t, ct)

print(t)
print(ct)

I introduced a function called “deep_clone”, which creates a complete duplicate of a table (useful with nested tables) so the original state of the primary table can then be used as a reference for the second loop.

1 Like
#9

now wait a minute, couldn’t you use table.clone()?

#10

If I recall correctly, table.clone creates a shallow copy of a table. The difference is that a deep copy duplicates all nested tables. Shallow copy does not, and only duplicates values on the root level of a table. Its child tables only get their reference passed (any change to a child table will reflect on all references of it).

1 Like
#11

If the value doesn’t exist and it is a table you should deep_clone it:

	for i,v in ct do -- iterates through campring table
		warn(i, v)
		if pt[i] == nil then -- if value does not exist
			if typeof(v) == "table" then
			    pt[i] = deep_clone(v)
			else
			    pt[i] = v -- adds value to table
			end
		else
		    if typeof(v) == "table" then -- if value is a table
			    if not (typeof(pt[i]) == "table") then
				    pt[i] = {} -- Overwrite to empty table to allow update to fill all missing details.
			    end
			    update(pt[i], v) -- Recusive?
		    end
		end
	end
#12

It’s not that, I mean that the function see’s the table inside the function arguments as nil, and not a table, which is odd because the variables prior to firing are referenced.

#13

If the function sees the parameter as nil, then you’re sending a nil value. There is no way a parameter will be interpreted as nil by the function unless it really is nil.

It’s not a problem with how the language works, it’s a problem within the code.

#14

It isnt, the code I gave you is the exact code that I used, its saying that ct is nil while it is clearly a table as referenced prior to firing

#15

By exact code, do you mean the code on the main post?

I got no errors with that code. Did you use a different table this time? What else have you done with the code?

#16

Im referring to this code that I tested with:

The function isnt repeating as I added a print to check if it was actually repeating, and it wasn’t as it only print once before the error.

Output:

-- prints prior to function
09:41:25.227   ▶ {...}  ▶ {...}  -  Server - Script:44 
-- function fired
09:41:25.228   ▶ {...}  ▶ {...}  -  Server - Script:2
09:41:25.228  E  -  Server - Script:4 -- print function
09:41:25.228   ▶ {...}  ▶ {...}  -  Server - Script:2 -- tables printed
-- error
09:41:25.228  'Workspace.Script:3: attempt to iterate over a nil value'  -  Server - Script:3

Edit: nevermind, it is actually only repeating once before the error.

#17

What update function were you using? Is it the original code or my revision? Both functions never cause an error.

#18

I found out what was happening, nevermind.

The prints are giving me a nil value inside the tables, and now I’m not sure how to fix them, I have checked if the table wasn’t nil, but somehow it doesnt work.
(Whoops, accidental reply)