Converting a string to its alphabetical counterpart

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#1

If the title wasn’t as informative as needed, this is what I’m trying to do:

local alphabet = {a=1,b=2,c=3}
local function convert(text)
	return print(alphabet[text])
end
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#2

Something like this should work, no need for numbers in the table since index of the letters can be used:

local alphabet = {"a","b","c","d","e","f"}

function convert(text)
	
	local str = string.split(text,"")
	local str2 = ""
	
	for i,v in pairs(str) do
		str2 ..= table.find(alphabet,str[i])
	end

	return print(str2)
end

convert("faded")
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#3

You could also use string.byte to get the numbers instead of the alphabet table, string.byte("a") = 97 while string.byte("A") = 65 so you would need to subtract 96 to get the 1, if you want both A and a to = 1 then just do string.lower as the first step in function.

#4

If I understood you right, do you want to get letters/strings in an order?

#5

I cannot tell everyone how much I appreciate them for their suggestions.

#6

Here is a way better and efficient way to do it using string manipulation

local function convert(text)
        local t = {}                                    
        local byte = string.byte
        local a_byte = byte('a')             
        
        for i = 1, #text do
                local n = byte(text, i, i) - a_byte + 1
                t[i] = tostring(n)                                         
        end     
        
        return table.concat(t)
end

print(convert("faded"))

And here is the best way to do it without generating any string stuff, way faster and memory efficient xD

local function convert(text)
        local n = 0
        local byte = string.byte
        local a_byte = byte('a')
        local factor = 1

        for i = #text, 1, -1 do
                local digit = byte(text, i, i) - a_byte + 1
                -- supports abcdefghi
                assert(digit < 10 and digit > 0)
                n = n + digit*factor
                factor = factor * 10
        end

        return n
end

print(convert("faded"))

I understand this 2 pieces of code would probably seems like magic to a beginner, but here is my own videos where I explained the math and logic behind the techniques I used here:

Benchmark (LuaJIT) for 1000000 iterations:

my first function (string manipulation): 0.596711 second
my second function (cool math lol): 0.039504 second

my second function took 6% of the time the first function took xD
I wouldn’t even compare the memory usage between them, since the first function have to store tables and strings, while my second function only store 2 numbers or so xD

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