pattern matching question

keszegh · August 2022

Hi guys, pattern matching is always a magic to me. I've wasted an hour on this issue, maybe you can solve faster:
given a string of the form:
number-spaces-number-spaces-number-optionalspaces-optionaltext(with possible spaces in it)
e.g.:
"100 100 60"
or
"60 250 80 this is it"

i want to extract the 3 numbers and the remainder as a string (or nil or "" it is is empty). what's the simplest way?
my best attempt so far:

string.match(text,"(%d*)%s*(%d*)%s*(%d*)%s?(.?*?)"))

which returns the numbers and the first letter of the remaining text. i don't understand why not all the remaining text though.

(i need this to read files in the gpl format, aka gimp palette)

keszegh · August 2022

btw i need the numbers as numbers and not as text, but i can convert them in a next step, so that's not an issue.

MoKaLux · August 2022

here is a snipet from Gideros obj loader, maybe this can help?

local function Split(str, delim, maxNb)
    -- Eliminate bad cases...
    if string.find(str, delim) == nil then return { str } end
	if maxNb == nil or maxNb < 1 then
		maxNb = 0 -- No limit
	end
	local result = {}
	local pat = "(.-)" .. delim .. "()"
	local nb = 0
	local lastPos
	for part, pos in string.gmatch(str, pat) do
		if #part>0 then
			nb = nb + 1
			result[nb] = part
			lastPos = pos
			if nb == maxNb then break end
		end
	end
	-- Handle the last field
	if nb ~= maxNb then result[nb + 1] = string.sub(str, lastPos) end
	return result
end

Then:

	for line in io.lines(path.."/"..file) do
		fld=Split(line," ",10)
		for i=1,#fld,1 do fld[i]=string.gsub(fld[i], "\r", "") end
		if (fld[2]~=nil) then fld[2]=string.gsub(fld[2], "\r", "") end
		if fld[1]=="newmtl" then mtl={} mtls[prefix..fld[2]]=mtl
		elseif fld[1]=="Kd" then mtl.kd={fld[2],fld[3],fld[4],1.0}
		elseif fld[1]=="d" then mtl.kd[4]=fld[2] -- alpha XXX
		elseif fld[1]=="map_Kd" then
		...
	end

keszegh · August 2022

thanks, but reverse engineering such a code is what is especially painful for me. i was hoping that someone can tell me what is the few characters i need to change in my one line code so that it works as i want.

MoKaLux · August 2022

The code reads each line and puts every "text" (separated by space " ") in a table.
Then after that you can do whatever you like with the values (fld[1], fld[2], ...).

fld=Split(line," ",10)
for i=1,#fld,1 do fld[i]=string.gsub(fld[i], "\r", "") end
if (fld[2]~=nil) then fld[2]=string.gsub(fld[2], "\r", "") end

rrraptor · August 2022

function split(str)
	str = str:gsub("%s+"," ") -- transform any sequance of whitespace characters (tabs, spaces) to a single white space
 
	-- empty string?
	if str:len() == 0 then 
		return {0, 0, 0}
	end
 
	local numbers, text = str:match("%s*([%d%s]*)(.*)") -- extract numbers and text
	local color = numbers:split(" ") -- extract numbers as separated elements
 
	-- convert string to number
	for i = 1, 3 do 
		color[i] = tonumber(color[i]) or 0
	end
 
	return color, text
end
 
local tests = {
	"255	255		255		hello world",
	"  10   10  10 some text here",
	"nothing here...",
	"10  10   10"
}
 
for i = 1, #tests do
	local colors, text = split(tests[i])
	print("Test #"..i)
	print(colors[1])
	print(colors[2])
	print(colors[3])
	print(text)
end

Pattern: https://regex101.com/r/RpwwBv/1

keszegh · August 2022

why is numbers:split(" ") a valid call?

keszegh · August 2022

str:match("%s*([%d%s]*)(.*)") seems to split at the wrong place if the text contains numbers as well.

rrraptor · August 2022

keszegh said:
why is numbers:split(" ") a valid call?

https://developer.roblox.com/en-us/api-reference/lua-docs/string

rrraptor · August 2022

@keszegh
if there is only 3 numbers:

function split(str)
	str = str:gsub("%s+"," ")
 
	if str:len() == 0 then 
		return {0, 0, 0}
	end
 
	local r, g, b, text = str:match("%s*(%d*)%s*(%d*)%s*(%d*)%s*(.*)")
 
	-- if there is no numbers (see test #4)
	if r == '' then 
		r = 0
		g = 0
		b = 0
	else
		r = tonumber(r)
		g = tonumber(g)
		b = tonumber(b)
	end
 
	return r, g, b, text
end
 
local tests = {
	"255	255		255		hello world",
	"  10   10  10 some text here",
	"  10   10  10 text with numbers 123",
	"nothing here...",
	"10  10   10"
}
 
for i = 1, #tests do
	local r,g,b, text = split(tests[i])
	print("Test #"..i)
	print(r,g,b)
	print(text)
	print(string.rep('-', 15))
end

keszegh · August 2022

works beautifully, thanks

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