Need help with a math function

[Mayron]

Hi,

I need to compare a number with a list of numbers and work out which one of the numbers in the list is closest to the one I want to compare. If there are two numbers that have the same amount of difference then pick the higher number. All numbers in this list will be unique.

Is there a function that can help me? I need recommendations on what to use or some help as I'm not brilliant with programming.

Basically I have this:
currentIndex = GetCurrentResolution()

and I need to compare the currentIndex with a list of numbers {7, 11, 12, 13, 15, 16}

Thank you for reading!

[Resike]

Why do you exactly need this?

[Malsomnus]

Looks pretty straightforward algorithm to me... go over the list, compare the numbers, save the best fit

[Mayron]

Originally Posted by Resike Why do you exactly need this?

So that it finds your current resolution and sees whether it is in the list of resolutions that the UI supports and if not then it picks the closest resolution to yours and sets the UI up accordingly. So that it may only need slightly adjusting.

[Resike]

local math = math
 
local x = 14
local y = {7, 11, 12, 13, 15, 16}
 
function ReturnStuff(n, t)
    local closest = t[#t]
    local closestId
    for i = 1, #t do
        if closest >= math.abs(t[i] - n) then
            closest = math.abs(t[i] - n)
            closestId = i
        end
    end
    return t[closestId]
end
 
print(ReturnStuff(x, y))

Edit: Try this.

[Mayron]

Originally Posted by Malsomnus Looks pretty straightforward algorithm to me... go over the list, compare the numbers, save the best fit

Is there some sort of function I could use to see if one number is closer to a number than another number?
Probably does not help that I have a massive head ache at the moment lol

EDIT: Thank you Resike! I will try using that

EDIT2: No that does not work Resike. Will look into another solution

[Seerah]

If this were me, I would just put the resolutions in a dropdown menu.

[Mayron]

Originally Posted by Seerah If this were me, I would just put the resolutions in a dropdown menu.

Well sadly I'm not you. I'm not that advanced with Lua yet haha. Otherwise yes that would solve everything but the way my addon works. Not sure how I would add a drop down box onto the artwork.

[Mayron]

Originally Posted by Resike --Code Edit: Try this.

Thank you very much for your work! That works perfectly Really appreciate your help!

[Vrul]

Originally Posted by Mayron Thank you very much for your work! That works perfectly Really appreciate your help!

Actually that code has errors in it. Other than the obvious, it assumes that the array you are passing in is sorted which was never a stated condition. This will fix the errors as well as that assumption:

local math_abs = math.abs

local resArray = { 7, 11, 12, 13, 15, 16 }
local resIndex = GetCurrentResolution()

local function GetClosestNumber(num, array)
    local id = 1
    local closest = math_abs(array[id] - num)
    for index = 2, #array do
        local delta = math_abs(array[index] - num)
        if delta < closest or (closest == delta and array[index] > array[id]) then
            closest, id = delta, index
        end
    end
    return array[id]
end

print(GetClosestNumber(resIndex, resArray))

If the array will always be pre-sorted then this is what you want:

local function GetClosestMatch(num, array)
    local id = 1
    local closest = math_abs(array[id] - num)
    for index = 2, #array do
        local delta = math_abs(array[index] - num)
        if delta < closest then
            closest, id = delta, index
        elseif delta == 0 or closest == delta then
            id = index
            break
        else
            break
        end
    end
    return array[id]
end

[Lombra]

Originally Posted by Vrul Actually that code has errors in it. Other than the obvious, it assumes that the array you are passing in is sorted which was never a stated condition.

Can you explain this? Because I don't see it. All I see is some references to table which should be t.

[Vrul]

Originally Posted by Lombra Can you explain this? Because I don't see it. All I see is some references to table which should be t.

As you pointed out there are a few references to table that should be t. The references to x in the function should be resolutionId, or resolutionId in the function definition should be changed to x. And like I stated it makes an assumption that was not stated as a known fact about the input. Going on that assumption though, the code makes an unnecessary extra for iteration (worst case) and has no early out (not worst case). It also makes a local reference to math while only using it to call math.abs instead of just making math.abs the local reference. The last two aren't errors, just pointing it out for those trying to learn.

[Resike]

Originally Posted by Vrul As you pointed out there are a few references to table that should be t. The references to x in the function should be resolutionId, or resolutionId in the function definition should be changed to x. And like I stated it makes an assumption that was not stated as a known fact about the input. Going on that assumption though, the code makes an unnecessary extra for iteration (worst case) and has no early out (not worst case). It also makes a local reference to math while only using it to call math.abs instead of just making math.abs the local reference. The last two aren't errors, just pointing it out for those trying to learn.

Well i assumed it's sorted, since the resoultion dropdown seems sorted, but yeah presorting the table, or your method would be better. However i still think my code is faster, despite the math calls and the extra for iterate, since you store an unneseccary delta variable inside the for loop which is more expensive.

Anyway something seems to be wrong with your functions because none of them is returning the right values.

[Phanx]

Originally Posted by Resike ... i still think my code is faster, despite the math calls and the extra for iterate, since you store an unneseccary delta variable inside the for loop which is more expensive.

wat?

Assigning a value to a variable N times is not more expensive than calling a function N extra times. The value is already taking up space in memory just by existing. Assigning it to a variable there costs basically nothing, whereas calling the same function to get the same value again is a complete waste of CPU time...

[Resike]

Originally Posted by Mayron Well sadly I'm not you. I'm not that advanced with Lua yet haha. Otherwise yes that would solve everything but the way my addon works. Not sure how I would add a drop down box onto the artwork.

If you want to use that version then:

print(UIDropDownMenu_GetSelectedID(Graphics_ResolutionDropDown))

[Vrul]

Originally Posted by Resike Anyway something seems to be wrong with your functions because none of them is returning the right values.

Yep, I forgot to change id to index when I copy-pasted math_abs(array[id] - num) from a couple lines up, it is fixed now.

Luckily Phanx already corrected you on the latest misinformation, but please quit making stuff up and posting it as fact. I'm not trying to be a bad guy here, you posting that stuff could really mislead someone trying to learn this stuff.

[Resike]

Originally Posted by Vrul Yep, I forgot to change id to index when I copy-pasted math_abs(array[id] - num) from a couple lines up, it is fixed now. Luckily Phanx already corrected you on the latest misinformation, but please quit making stuff up and posting it as fact. I'm not trying to be a bad guy here, you posting that stuff could really mislead someone trying to learn this stuff.

Sorry, my bad.

[Lombra]

I meant the bit about the assumption that the array is sorted. I don't see anything here that the sorting of the array would have any impact on:

local math = math
 
local x = 14
local y = {7, 11, 12, 13, 15, 16}
 
function ReturnStuff(n, t)
    local closest = t[#t]
    local closestId
    for i = 1, #t do
        if closest >= math.abs(t[i] - n) then
            closest = math.abs(t[i] - n)
            closestId = i
        end
    end
    return t[closestId]
end
 
print(ReturnStuff(x, y))

This is the snippet you were commenting, yes? Pretty sure that's how it looked when I first posted bar the table -> t.

[Vrul]

Originally Posted by Lombra I meant the bit about the assumption that the array is sorted. I don't see anything here that the sorting of the array would have any impact on:

Reverse the sample array and you will get 13 instead of 15, which is not the desired stated behavior.

Originally Posted by Lombra This is the snippet you were commenting, yes? Pretty sure that's how it looked when I first posted bar the table -> t.

The n was instead the variable x from outside the function, making the passed value to search for be ignored. Sure the code as posted worked but taking the function, the whole point of this thread, and pasting it into another addon would not work as intended.

[Lombra]

Ok, I missed the bit about needing to default to the higher value if equal.