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✓ ANSWER ACCEPTED

how to get the value of an nil index?

Asked 247 views1 answers

what im trying to do is getting the value of an nil index, like if there was only 3 values in the table and i tried to index a 4th index in the table. it would return the 1st value; index a 5th index = 2nd value. i know i can just subtract the index by the length of the table, but that wont work for most indexes.

local array = {10,30,40,50,60}

print(array[6]) -- i want it to print the first index which is 10
print(array[7]) -- 30
print(array[8]) -- 40

-- i can only index with a nil index up to a 10th index until it returns nil using index - #array

print(array[11-#array]) -- nil
print(array[10-#array]) -- 60
AnonymousEdited

2 comments

0

Nil indices have no value.

Anonymous#
0

can u read my question again

Anonymous#

1 answer

✓ Accepted answer

Whenever you need a value that wraps around like you just mentioned, the first thing that should come to mind is the modulo operator % also called the remainder operator. The modulo operator receives two operands and returns the remainder when the first is divided by the second. For example, 17 % 5 = 2 and 5.6 % 1 = 0.6. This logic leads to the following solution:

local array = {10 , 30 , 40 , 50 , 60}
       
function wrap(n , x)
	return (n - 1) % x + 1 --% has higher precedence then +
end
print(array[wrap(5 , #array)]) --60
print(array[wrap(234 , #array)]) --50
print(array[wrap(-2 , #array)]) --40

If we want, we can also use metatables to further abstract this logic away:

local array = setmetatable({10 , 30 , 40 , 50 , 60} , {
	__index = function(array , i)
		return array[wrap(i , #array)]
	end;
	__newindex = function(array , i , v)
		array[wrap(i , #array)] = v
	end;
})
AnonymousPermalink

2 comments

0

thanks

Anonymous#
0

no problem

Anonymous#

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