I'm learning Lua and probably don't have a great grasp on how the language works but I'm trying to create a split function for the string library:
string.split = function(str, delimiter)
-- A function which splits a string by a delimiter
values = {}
currentValue = ""
for i = 1, string.len(str) do
local character = string.sub(str, i, i)
if(character == delimiter) then
table.insert(values,currentValue)
currentValue = ""
else
currentValue = currentValue..character
end
end
-- clean up last item
table.insert(values,currentValue)
return vaules
end
values is not nil if I print it out before the return, but if I call t = string.split("hello world", " "), t will be nil. I'm not quite sure why my table is disappearing
You have a typo in your return statement.
vaules
Instead of values.
vaules is nil of course.
Another advice: make variables local wherever possible.
Related
In javascript we can do the following:
var someString = `some ${myVar} string`
I have the following lua code, myVar is a number that needs to be in the square brackets:
splash:evaljs('document.querySelectorAll("a[title*=further]")[myVar]')
Function that fits you description is string.format:
splash:evaljs(string.format('document.querySelectorAll("a[title*=further]")[%s]', myVar))
It is not as verbose as ${}. It is more of a good old (and hated) sprintf.
I have written an emulation of Python's f'' strings, which is a set of functions you can hide inside a require file. So, if you like Python's f'' strings, this may be what you're looking for.
(If anyone finds errors, please notify.)
It's quite big compared to the other solution, but if you hide the bulk in a library, then its use is more compact and readable, IMO.
With this library you can do the following, for example:
require 'f_strings'
a = 12345
print(f'Number: {a}, formatted with two decimals: {a::%.2f}')
-- Number: 12345, formatted with two decimals: 12345.00
Note the use of Lua string.format formatting codes, and the use of double colon (instead of Python's single colon) for format specifiers because of Lua's use of colon for methods.
I have extracted only the relevant functions from a larger library. Although some optimizations may be possible for this specific use case, I leave them unchanged as they are general purpose and may also be useful for other purposes.
And here's the required library (placed somewhere in your Lua libraries folder):
-- f_strings.lua ---
unpack = table.unpack or unpack
--------------------------------------------------------------------------------
-- Escape special pattern characters in string to be treated as simple characters
--------------------------------------------------------------------------------
local
function escape_magic(s)
local MAGIC_CHARS_SET = '[()%%.[^$%]*+%-?]'
if s == nil then return end
return (s:gsub(MAGIC_CHARS_SET,'%%%1'))
end
--------------------------------------------------------------------------------
-- Returns iterator to split string on given delimiter (multi-space by default)
--------------------------------------------------------------------------------
function string:gsplit(delimiter)
if delimiter == nil then return self:gmatch '%S+' end --default delimiter is any number of spaces
if delimiter == '' then return self:gmatch '.' end
if type(delimiter) == 'number' then --break string in equal-size chunks
local index = 1
local ans
return function()
ans = self:sub(index,index+delimiter-1)
if ans ~= '' then
index = index + delimiter
return ans
end
end
end
if self:sub(-#delimiter) ~= delimiter then self = self .. delimiter end
return self:gmatch('(.-)'..escape_magic(delimiter))
end
--------------------------------------------------------------------------------
-- Split a string on the given delimiter (comma by default)
--------------------------------------------------------------------------------
function string:split(delimiter,tabled)
tabled = tabled or false --default is unpacked
local ans = {}
for item in self:gsplit(delimiter) do
ans[#ans+1] = item
end
if tabled then return ans end
return unpack(ans)
end
--------------------------------------------------------------------------------
function copy(t) --returns a simple (shallow) copy of the table
if type(t) == 'table' then
local ans = {}
for k,v in next,t do ans[ k ] = v end
return ans
end
return t
end
--------------------------------------------------------------------------------
function eval(expr,vars)
--evaluate a string expression with optional variables
if expr == nil then return end
vars = vars or {}
assert(type(expr) == 'string','String expected as 1st arg')
assert(type(vars) == 'table','Variable table expected as 2nd arg')
local env = {abs=math.abs,acos=math.acos,asin=math.asin,atan=math.atan,
atan2=math.atan2,ceil=math.ceil,cos=math.cos,cosh=math.cosh,
deg=math.deg,exp=math.exp,floor=math.floor,fmod=math.fmod,
frexp=math.frexp,huge=math.huge,ldexp=math.ldexp,log=math.log,
max=math.max,min=math.min,modf=math.modf,pi=math.pi,pow=math.pow,
rad=math.rad,random=math.random,randomseed=math.randomseed,
sin=math.sin,sinh=math.sinh,sqrt=math.sqrt,tan=math.tan,
tanh=math.tanh}
for name,value in pairs(vars) do env[name] = value end
local a,b = pcall(load('return '..expr,nil,'t',env))
if a == false then return nil,b else return b end
end
--------------------------------------------------------------------------------
-- f'' formatted strings like those introduced in Python v3.6
-- However, you must use Lua style format modifiers as with string.format()
--------------------------------------------------------------------------------
function f(s)
local env = copy(_ENV) --start with all globals
local i,k,v,fmt = 0
repeat
i = i + 1
k,v = debug.getlocal(2,i) --two levels up (1 level is this repeat block)
if k ~= nil then env[k] = v end
until k == nil
local
function go(s)
local fmt
s,fmt = s:sub(2,-2):split('::')
if s:match '%b{}' then s = (s:gsub('%b{}',go)) end
s = eval(s,env)
if fmt ~= nil then
if fmt:match '%b{}' then fmt = eval(fmt:sub(2,-2),env) end
s = fmt:format(s)
end
return s
end
return (s:gsub('%b{}',go))
end
I'm confused with the concepts of stateless iterators. As an exercise I write an iterator to print all non-empty substrings of a given string. The code is as follows.
local function iter(state, i)
local str = state.str
if type(str) ~= "string" or str == "" then return nil end
if state.ending > #str then return nil end
local start = state.start
local ending = state.ending
if start == ending then
state.ending = ending + 1
state.start = 1
else
state.start = start + 1
end
return string.sub(str, start, ending)
end
function allSubstrings(str)
return iter, { str = str, start = 1, ending = 1 }, nil
end
for substr in allSubstrings("abcd123") do
print(substr)
end
I use a table { str = str, start = 1, ending = 1 } as the so-called invariant state, but I have to change the fields in this table in the iter local function. So is this iterator stateless or with complex states? If it's not stateless, is there a way to implement this functionality with a stateless iterator?
Thank you.
The PIL-chapter about stateless iterators states:
As the name implies, a stateless iterator is an iterator that does not keep any state by itself. Therefore, we may use the same stateless iterator in multiple loops, avoiding the cost of creating new closures.
In code that means that both for loops in:
f, s, var = pairs( t )
for k,v in f, s, var do print( k, v ) end
for k,v in f, s, var do print( k, v ) end
should produce the same output. This only works if neither the invariant state s nor any upvalues of the iterator function f change during the iteration, or else the second for loop would have different starting conditions than the first loop.
So, no, your iterator is not a stateless iterator because you change the invariant state during iteration.
There is a way to make your iterator stateless (and the popular Lua library luafun uses this technique extensively): keep all mutable state in the loop control variable var (even if you need to allocate a fresh table in each allocation step):
local function iter( str, var )
if type( str ) ~= "string" or str == "" then return nil end
if var[ 2 ] > #str then return nil end
local start, ending = var[ 1 ], var[ 2 ]
if start == ending then
return { 1, ending+1 }, string.sub( str, start, ending )
else
return { start+1, ending }, string.sub( str, start, ending )
end
end
function allSubstrings2( str )
return iter, str, { 1, 1 }
end
for _,substr in allSubstrings2( "abcd123" ) do
print( substr )
end
Drawbacks are that the first iteration variable var (the loop control variable) has no useful meaning for the user of the iterator, and since you have to allocate a table for each iteration step, "avoiding the cost of creating new closures" for another loop doesn't matter much.
luafun does it anyway, because it does not have the ability to recreate an iterator tuple (it is passed via function arguments from outside code), and for some algorithms you absolutely need to run the same iteration multiple times.
An alternative to this approach would be to concentrate all mutable state in the "invariant state" s (all upvalues to f must be immutable), and provide a way to copy/clone this state for later iterations:
f, s, var = allSubstrings("abcd123")
s2 = clonestate( s )
for str in f, s, var do print( str ) end
for str in f, s2, var do print( str ) end
This is still not a stateless iterator, but it is more memory-efficient than the stateless iterator with heap-allocated loop control variable, and it allows you to restart an iteration.
This is not a stateless iterator, and is indeed an iterator with complex state.
In stateless iterators there is only one control variable, and it should be treated as a pure value throughout the iterator.
You could consider using closures to implement this. Not quite stateless, but does use upvalues over table lookups, which should be more efficient.
local function allSubstrings (str)
if type(str) ~= "string" or str == "" then
return function () end -- NOP out on first iteration
end
local length = #str
local start, ending = 1, 1
return function ()
if ending > length then return nil end
local st, ed = start, ending
if start == ending then
ending = ending + 1
start = 1
else
start = start + 1
end
return string.sub(str, st, ed)
end
end
for substr in allSubstrings("abcd123") do
print(substr)
end
PIL book calls that 'Iterators with Complex State'
http://www.lua.org/pil/7.4.html
I'd like to format a number to look like 1,234 or 1,234,432 or 123,456,789, you get the idea. I tried doing this as follows:
function reformatint(i)
local length = string.len(i)
for v = 1, math.floor(length/3) do
for k = 1, 3 do
newint = string.sub(mystring, -k*v)
end
newint = ','..newint
end
return newint
end
As you can see, a failed attempt, my problem is that I can't figure out what the error is because the program I am running this in refuses to report an error back to me.
Here's a function that takes negative numbers, and fractional parts into account:
function format_int(number)
local i, j, minus, int, fraction = tostring(number):find('([-]?)(%d+)([.]?%d*)')
-- reverse the int-string and append a comma to all blocks of 3 digits
int = int:reverse():gsub("(%d%d%d)", "%1,")
-- reverse the int-string back remove an optional comma and put the
-- optional minus and fractional part back
return minus .. int:reverse():gsub("^,", "") .. fraction
end
assert(format_int(1234) == '1,234')
assert(format_int(1234567) == '1,234,567')
assert(format_int(123456789) == '123,456,789')
assert(format_int(123456789.1234) == '123,456,789.1234')
assert(format_int(-123456789.) == '-123,456,789')
assert(format_int(-123456789.1234) == '-123,456,789.1234')
assert(format_int('-123456789.1234') == '-123,456,789.1234')
print('All tests passed!')
Well, let's take this from the top down. First of all, it's failing because you've got a reference error:
...
for k = 1, 3 do
newint = string.sub(mystring, -k*v) -- What is 'mystring'?
end
...
Most likely you want i to be there, not mystring.
Second, while replacing mystring with i will fix the errors, it still won't work correctly.
> =reformatint(100)
,100
> =reformatint(1)
,000
That's obviously not right. It seems like what you're trying to do is go through the string, and build up the new string with the commas added. But there are a couple of problems...
function reformatint(i)
local length = string.len(i)
for v = 1, math.floor(length/3) do
for k = 1, 3 do -- What is this inner loop for?
newint = string.sub(mystring, -k*v) -- This chops off the end of
-- your string only
end
newint = ','..newint -- This will make your result have a ',' at
-- the beginning, no matter what
end
return newint
end
With some rework, you can get a function that work.
function reformatint(integer)
for i = 1, math.floor((string.len(integer)-1) / 3) do
integer = string.sub(integer, 1, -3*i-i) ..
',' ..
string.sub(integer, -3*i-i+1)
end
return integer
end
The function above seems to work correctly. However, it's fairly convoluted... Might want to make it more readable.
As a side note, a quick google search finds a function that has already been made for this:
function comma_value(amount)
local formatted = amount
while true do
formatted, k = string.gsub(formatted, "^(-?%d+)(%d%d%d)", '%1,%2')
if (k==0) then
break
end
end
return formatted
end
You can do without loops:
function numWithCommas(n)
return tostring(math.floor(n)):reverse():gsub("(%d%d%d)","%1,")
:gsub(",(%-?)$","%1"):reverse()
end
assert(numWithCommas(100000) == "100,000")
assert(numWithCommas(100) == "100")
assert(numWithCommas(-100000) == "-100,000")
assert(numWithCommas(10000000) == "10,000,000")
assert(numWithCommas(10000000.00) == "10,000,000")
The second gsub is needed to avoid -,100 being generated.
I remember discussing about this in the LÖVE forums ... let me look for it...
Found it!
This will work with positive integers:
function reformatInt(i)
return tostring(i):reverse():gsub("%d%d%d", "%1,"):reverse():gsub("^,", "")
end
On the link above you may read details about implementation.
Good evening
Will you help me solve this problem?
ERROR: race/util_server.lua:440: attempt to index local 'self' (a nil value)
function string:split(separator)
if separator == '.' then
separator = '%.'
end
local result = {}
for part in self:gmatch('(.-)' .. separator) do
result[#result+1] = part
end
result[#result+1] = self:match('.*' .. separator .. '(.*)$') or self
return result
end
You're probably calling it wrong.
function string:split(separator)
Is short hand for:
function string.split(self, separator)
Given a string and separator:
s = 'This is a test'
separator = ' '
You need to call it like this:
string.split(s, separator)
Or:
s:split(separator)
If you call it like this:
s.split(separator)
You're failing to provide a value for the self argument.
Side note, you can write split more simply like this:
function string:split(separators)
local result = {}
for part in self:gmatch('[^'..separators..']+') do
result[#result + 1] = part
end
return result
end
This has the disadvantage that you can't used multi-character strings as delimiters, but the advantage that you can specify more than one delimiter. For instance, you could strip all the punctuation from a sentence and grab just the words:
s = 'This is an example: homemade, freshly-baked pies are delicious!'
for _,word in pairs(s:split(' :.,!-')) do
print(word)
end
Output:
This
is
an
example
homemade
freshly
baked
pies
are
delicious
I have the following function in Lua:
function iffunc(k,str,str1)
if k ~= 0 then
return str .. k .. (str1 or "")
end
end
This function allows me to check if value k is populated or not. I'm actually using it to determine if I want to display something that has zero value. My problem is this: I'm trying to concatenate a string of iffunc(), but since some of the values are 0, it returns an error of trying to concatenate a nil value. For instance:
levellbon = iffunc(levellrep["BonusStr"],"#wStr#r{#x111","#r}") .. iffunc(levellrep["BonusInt"],"#wInt#r{#x111","#r}") .. iffunc(levellrep["BonusWis"],"#wWis#r{#x111","#r}")
If any of the table values are 0, it'll return the error. I could easily put 'return 0' in the iffunc itself; however, I don't want a string of 000, either. So how can I work it where no matter which values are nil, I won't get that error? Ultimately, I'm going to do an iffunc on the levellbon variable to see if that's populated or not, but I've got that part figured out. I just need to get past this little hurdle right now. Thanks!
I'd do this:
function iffunc(k,str,str1)
if k == 0 then return "" end
return str .. k .. (str1 or "")
end
You should add an else statement in the function, where you return an empty string ("").