LÖVE

Posted: **Thu Feb 21, 2013 3:00 am**

Hi,

I'm trying to compare all entries of a table against all entries of another, any identical entries then being removed from the second table. The problem is a for loop will only let me check whatever entries the iterator happens to correspond to at that moment. I'm looking to compare every single entry of both tables against one another.

Apologies if this is really simple, but it's way past my bedtime and this has me stumped.

Thanks in advance!

Posted: **Thu Feb 21, 2013 3:27 am**

What about a double for-loop?

Code: Select all

for i=1, #table1 do
    partA = table1[i]
    for j=1, #table2 do
        partB = table2[j]
        if partA == partB then table.remove(table2, j) end
    end
end

If someone haven't noticed, that's almost the same as my collision-detection loop, minus the optimization since both tables might not have the same number of indices.

Posted: **Thu Feb 21, 2013 3:40 am**

Thanks for the quick reply.

Just to make sure I understand I'll get more specific as to what my problem is:

I have two tables filled with objects that may or may not have the same index value at any given time. The objects are cards with a suit and number attribute.
The check will be if the Suit and Number of the entry in the first table is identical to that of the second then remove said entry from the second table.

Code: Select all


for i = 1, #table1 do
	for j = 1, #table2 do
		if( table1[i].n  == table[j].n and table1[i].s == table2[j].s ) then
			table.remove(table2, j)
		end
	end
end

Will this code do the trick?
Thanks again for the help.

Posted: **Thu Feb 21, 2013 3:44 am**

Since you're removing things, I highly recommend iterating backwards so that table.remove won't mess you up. Like so:

Code: Select all

for i=#table1, 1, -1 do
   for j=#table2, 1, -1 do    -- backwards!
      if( table1[i].n  == table[j].n and table1[i].s == table2[j].s ) then
         table.remove(table2, j)
      end
   end
end

Otherwise you may end up skipping entries, and getting other subtly wrong behavior.

Posted: **Thu Feb 21, 2013 3:54 am**

That's great advice, thank you.

While I'm on the subject of for loops I may as well ask: If I return a table entry 'i' during a for loop will that automatically end the loop? Or will it keep on looping and returning until it's defined stopping point?

Posted: **Thu Feb 21, 2013 4:02 am**

Using a "return" will take you out of whatever function you're in. If you want to exit just the innermost loop, you can use "break". For further reading, check out http://www.lua.org/manual/5.1/manual.html#2.4.4.

Posted: **Thu Feb 21, 2013 4:11 am**

I'll take a look.

Thanks for your help, it was really useful!

LÖVE

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