Finding the Closest Number to a Given One in an Array

[MartinFlikter (Flikter)]

Hello!

How would I create a function which finds and returns the closest number to a given one in an array?
So let’s say I had an array with the values of 5, 2, 3 and 8 and I wanted to get the closest number to 4.
So that’ll return 5.

[starmaq]

This is a simple algorithm, looping through the array, keeping track of the closest number to 4 so far, seeing if the next number has a smaller difference becoming the new closest one. At the end the number that ended in the variable we used to keep track, is the closest.

local closest = math.huge
local number = 4

for _, otherNumber in pairs(array) do
    if math.abs(number - otherNumber) < math.abs(number - closest) then
        closest = otherNumber
    end
end

print(number)

The closest variable keeping track of the current closest number is initialized as math.huge, this is a common pattern. The idea is if I did math.abs(4-math.huge), the result would always be math.huge, which is guaranteed to be larger than any other number in the array, and hence guaranteed to not be the end result. It’s a nice way to not add a check to see if there was not closest, in which case the current number is automatically the current closest.

math.abs(a-b) will basically find the distance between two numbers, mind you the distance, and not the difference. The difference between 2 and 4 is -2, assuming you mean 2-4 = -2, but the distance is 2. If we did not abs, then 8 would be considered closer, since 8-4 = 4 > -2, which is not the case.

[MartinFlikter (Flikter)]

I see, never mind me wanting to return 3, 5 works for my use case. Thank you for your detailed explanation, you have a very clever method!

[Forummer]

Rounding values to the nearest one in a table

local function RoundToNearestTableValue(Table, Number) table.sort(Table) local ClosestValue, ClosestDifference = nil, math.huge for Index, Value in ipairs(Table) do local Difference = math.abs(Number - Value) if Difference > ClosestDifference then continue end ClosestDifference = Difference ClosestValue = Value end return ClosestValue end local Result = RoundToNearestTableValue({1, 5, 9}, 6) print(Result) --5 This can be cut down even further. local function RoundToNearestTableVa…

[MartinFlikter (Flikter)]

My question has already been answered, but thank you for your reply!

[Forummer]

I know, I’m just reminding you that you should use the search feature before creating a thread.

[MartinFlikter (Flikter)]

I did use it! But I didn’t find that post.

[Forummer]

That’s strange because I searched for threads using the same keywords you’ve used in this thread’s title and found the following.

Getting a number nearest to the selected Number

--Variables local Values = {3, 8} local Answer = 10 for i = 1, #Values do Values[i] = {Values[i], math.abs(Answer - Values[i])} --3 = {3,7} --8 = {8,2} end table.sort(Values,function(a, b) return a[2] < b[2] end) for i = 1, #Values do print(Values[i][1]) end This would print those numbers from the closest one to 10. [Answer], you could modify it. Hope it could help.

Finding the closest number from a table

May I ask, why are you using pairs instead of ipairs for array iteration? Alternativaly create a function for this just in case. function find_closest(number_table, value) local closest; local closest_diff; for _, n in ipairs(number_table) do if math.abs(n - value) < closest then closest, closest_diff = n, math.abs(n - value); end; end; return closest; end;

How to round to the nearest number in a table

Here you go. Next time, a bit more research perhaps? Doesn’t hurt, but glad to help.

[MartinFlikter (Flikter)]

Yeah. When originally searching, I didn’t search for those exact titles. Mostly searched for what my title is. The search results I saw weren’t of much use.