Reputation: 39467
Split string in Lua
How do I split a string? There doesn't seem to be a built-in function for this.
Upvotes: 233
Views: 469865
Answers (23)
Reputation: 2786
I would say that the best answer I know about right now is to consider Penlight as a Lua’s standard library and use https://lunarmodules.github.io/Penlight/libraries/pl.stringx.html#split
Upvotes: 0
Reputation:
Use the gmatch() function to capture strings which contain at least one character of anything other than the desired separator. The separator is any whitespace (%s in Lua) by default:
function mysplit(inputstr, sep)
if sep == nil then
sep = "%s"
end
local t = {}
for str in string.gmatch(inputstr, "([^"..sep.."]+)") do
table.insert(t, str)
end
return t
end
Upvotes: 185
Reputation:
this function extends string with split function 'python like'.
-- string functions utilities
string.split=function(self,sep,limit)
if sep==nil then
sep=" "
end
local _table = {}
local _string = ''
local x = 0 -- separation counter
for i=1,#self do
local char=string.sub(self,i,i) -- get character 'i' in string
if limit==nil then
-- unlimited separations
if char == sep then
-- separation found, insert string in table and 'reset' string to store next world
table.insert(_table,_string)
_string=""
else
_string = _string .. char -- store no separation character to store later
if i==#self then
-- last character in string, just add its remain to table
table.insert(_table,_string)
end
end
elseif type(limit)=="number" then
-- limited separations
if char == sep then
-- separation character found
x=x+1 -- increment separator count
if x<=limit then
-- while separator count <= limit, add _string to _table, and reset _string to next world
table.insert(_table,_string)
_string=""
else
-- separator counter limit pass, now just concat chars to the last string
_string = _string .. sep
end
else
-- no char seprator, concat char to string and insert in table if last char
_string = _string .. char
if i==#self then
table.insert(_table,_string)
end
end
end
end
-- return splitted table
return _table
end
usage:
msg='my favorite string'
msg=msg:split(' ',1)
this will result in table {'my','favorite string'} as expected!
Upvotes: 0
Reputation: 585
a way not seen in others
function str_split(str, sep)
if sep == nil then
sep = '%s'
end
local res = {}
local func = function(w)
table.insert(res, w)
end
string.gsub(str, '[^'..sep..']+', func)
return res
end
Upvotes: 7
Reputation: 586
The way to split a string to two strings in given position:
str1 = "helloworld"
str2 = ""
index = 5
str1, str2 = string.sub(str1, 1, index), string.sub(str1, index+1, -1)
print (str1, str2) -- hello world
Upvotes: 0
Reputation: 145
Cleanest/simplest solution yet? For splitting on whitespace, that is.
function(argstr)
local args = {}
for v in string.gmatch(argstr, "%S+") do
table.insert(args, v)
end
return args
end
Upvotes: 0
Reputation: 3075
There's an example (unexpandTabs) at the end of the Replacements section of Programming in Lua, 4th Ed., Chapter 10, that uses the SOH character (\1) to mark tab columns for later processing. I thought that was a neat idea, so I adapted it to the "match everything except a delimiter character" ideas that many of the answers here use. By preprocessing the input string to replace all matches with \1, we can support arbitrary delimiter patterns, which is something only some answers do, e.g. @norman-ramsey's excellent answer.
I also included an exclude_empty parameter with default behavior just for fun.
Obviously this will produce bad output if the input string contains \1, but that seems extremely unlikely in any case outside of specialized protocol exchanges.
function string:split(pat, exclude_empty)
pat = pat or "%s+"
self = self:gsub(pat, "\1")
local res = {}
for match in self:gmatch("([^\1]" .. (exclude_empty and "+" or "*") .. ")") do
res[#res + 1] = match
end
return res
end
Upvotes: 0
Reputation: 88
For those coming from the exercice 10.1 of the "Programming in Lua" book, it seems clear that we could not use notion explained later in the book (iterator) and that the function should take more than a single char seperator.
The split() is a trick to get pattern to match what is not wanted (the split) and return an empty table on empty string. The return of plainSplit() is more like the split in other language.
magic = "([%%%.%(%)%+%*%?%[%]%^%$])"
function split(str, sep, plain)
if plain then sep = string.gsub(sep, magic, "%%%1") end
local N = '\255'
str = N..str..N
str = string.gsub(str, sep, N..N)
local result = {}
for word in string.gmatch(str, N.."(.-)"..N) do
if word ~= "" then
table.insert(result, word)
end
end
return result
end
function plainSplit(str, sep)
sep = string.gsub(sep, magic, "%%%1")
local result = {}
local start = 0
repeat
start = start + 1
local from, to = string.find(str, sep, start)
from = from and from-1
local word = string.sub(str, start, from, true)
table.insert(result, word)
start = to
until start == nil
return result
end
function tableToString(t)
local ret = "{"
for _, word in ipairs(t) do
ret = ret .. '"' .. word .. '", '
end
ret = string.sub(ret, 1, -3)
ret = ret .. "}"
return #ret > 1 and ret or "{}"
end
function runSplit(func, title, str, sep, plain)
print("\n" .. title)
print("str: '"..str.."'")
print("sep: '"..sep.."'")
local t = func(str, sep, plain)
print("-- t = " .. tableToString(t))
end
print("\n\n\n=== Pattern split ===")
runSplit(split, "Exercice 10.1", "a whole new world", " ")
runSplit(split, "With trailing seperator", " a whole new world ", " ")
runSplit(split, "A word seperator", "a whole new world", " whole ")
runSplit(split, "Pattern seperator", "a1whole2new3world", "%d")
runSplit(split, "Magic characters as plain seperator", "a$.%whole$.%new$.%world", "$.%", true)
runSplit(split, "Control seperator", "a\0whole\1new\2world", "%c")
runSplit(split, "ISO Time", "2020-07-10T15:00:00.000", "[T:%-%.]")
runSplit(split, " === [Fails] with \\255 ===", "a\255whole\0new\0world", "\0", true)
runSplit(split, "How does your function handle empty string?", "", " ")
print("\n\n\n=== Plain split ===")
runSplit(plainSplit, "Exercice 10.1", "a whole new world", " ")
runSplit(plainSplit, "With trailing seperator", " a whole new world ", " ")
runSplit(plainSplit, "A word seperator", "a whole new world", " whole ")
runSplit(plainSplit, "Magic characters as plain seperator", "a$.%whole$.%new$.%world", "$.%")
runSplit(plainSplit, "How does your function handle empty string?", "", " ")
output
=== Pattern split ===
Exercice 10.1
str: 'a whole new world'
sep: ' '
-- t = {"a", "whole", "new", "world"}
With trailing seperator
str: ' a whole new world '
sep: ' '
-- t = {"a", "whole", "new", "world"}
A word seperator
str: 'a whole new world'
sep: ' whole '
-- t = {"a", "new world"}
Pattern seperator
str: 'a1whole2new3world'
sep: '%d'
-- t = {"a", "whole", "new", "world"}
Magic characters as plain seperator
str: 'a$.%whole$.%new$.%world'
sep: '$.%'
-- t = {"a", "whole", "new", "world"}
Control seperator
str: 'awholenewworld'
sep: '%c'
-- t = {"a", "whole", "new", "world"}
ISO Time
str: '2020-07-10T15:00:00.000'
sep: '[T:%-%.]'
-- t = {"2020", "07", "10", "15", "00", "00", "000"}
=== [Fails] with \255 ===
str: 'a�wholenewworld'
sep: ''
-- t = {"a"}
How does your function handle empty string?
str: ''
sep: ' '
-- t = {}
=== Plain split ===
Exercice 10.1
str: 'a whole new world'
sep: ' '
-- t = {"a", "whole", "new", "world"}
With trailing seperator
str: ' a whole new world '
sep: ' '
-- t = {"", "", "a", "", "whole", "", "", "new", "world", "", ""}
A word seperator
str: 'a whole new world'
sep: ' whole '
-- t = {"a", "new world"}
Magic characters as plain seperator
str: 'a$.%whole$.%new$.%world'
sep: '$.%'
-- t = {"a", "whole", "new", "world"}
How does your function handle empty string?
str: ''
sep: ' '
-- t = {""}
Upvotes: 1
Reputation: 1455
I found that many of the other answers had edge cases which failed (eg. when given string contains #, { or } characters, or when given a delimiter character like % which require escaping). Here is the implementation that I went with instead:
local function newsplit(delimiter, str)
assert(type(delimiter) == "string")
assert(#delimiter > 0, "Must provide non empty delimiter")
-- Add escape characters if delimiter requires it
delimiter = delimiter:gsub("[%(%)%.%%%+%-%*%?%[%]%^%$]", "%%%0")
local start_index = 1
local result = {}
while true do
local delimiter_index, _ = str:find(delimiter, start_index)
if delimiter_index == nil then
table.insert(result, str:sub(start_index))
break
end
table.insert(result, str:sub(start_index, delimiter_index - 1))
start_index = delimiter_index + 1
end
return result
end
Upvotes: 0
Reputation: 49
Here is a routine that works in Lua 4.0, returning a table t of the substrings in inputstr delimited by sep:
function string_split(inputstr, sep)
local inputstr = inputstr .. sep
local idx, inc, t = 0, 1, {}
local idx_prev, substr
repeat
idx_prev = idx
inputstr = strsub(inputstr, idx + 1, -1) -- chop off the beginning of the string containing the match last found by strfind (or initially, nothing); keep the rest (or initially, all)
idx = strfind(inputstr, sep) -- find the 0-based r_index of the first occurrence of separator
if idx == nil then break end -- quit if nothing's found
substr = strsub(inputstr, 0, idx) -- extract the substring occurring before the separator (i.e., data field before the next delimiter)
substr = gsub(substr, "[%c" .. sep .. " ]", "") -- eliminate control characters, separator and spaces
t[inc] = substr -- store the substring (i.e., data field)
inc = inc + 1 -- iterate to next
until idx == nil
return t
end
This simple test
inputstr = "the brown lazy fox jumped over the fat grey hen ... or something."
sep = " "
t = {}
t = string_split(inputstr,sep)
for i=1,15 do
print(i, t[i])
end
Yields:
--> t[1]=the
--> t[2]=brown
--> t[3]=lazy
--> t[4]=fox
--> t[5]=jumped
--> t[6]=over
--> t[7]=the
--> t[8]=fat
--> t[9]=grey
--> t[10]=hen
--> t[11]=...
--> t[12]=or
--> t[13]=something.
Upvotes: -1
Reputation: 504
Super late to this question, but in case anyone wants a version that handles the amount of splits you want to get.....
-- Split a string into a table using a delimiter and a limit
string.split = function(str, pat, limit)
local t = {}
local fpat = "(.-)" .. pat
local last_end = 1
local s, e, cap = str:find(fpat, 1)
while s do
if s ~= 1 or cap ~= "" then
table.insert(t, cap)
end
last_end = e+1
s, e, cap = str:find(fpat, last_end)
if limit ~= nil and limit <= #t then
break
end
end
if last_end <= #str then
cap = str:sub(last_end)
table.insert(t, cap)
end
return t
end
Upvotes: 3
Reputation: 397
Depending on the use case, this could be useful. It cuts all text either side of the flags:
b = "This is a string used for testing"
--Removes unwanted text
c = (b:match("a([^/]+)used"))
print (c)
Output:
string
Upvotes: -3
Reputation:
You could use penlight library. This has a function for splitting string using delimiter which outputs list.
It has implemented many of the function that we may need while programming and missing in Lua.
Here is the sample for using it.
>
> stringx = require "pl.stringx"
>
> str = "welcome to the world of lua"
>
> arr = stringx.split(str, " ")
>
> arr
{welcome,to,the,world,of,lua}
>
Upvotes: 6
Reputation: 6237
A lot of these answers only accept single-character separators, or don't deal with edge cases well (e.g. empty separators), so I thought I would provide a more definitive solution.
Here are two functions, gsplit and split, adapted from the code in the Scribunto MediaWiki extension, which is used on wikis like Wikipedia. The code is licenced under the GPL v2. I have changed the variable names and added comments to make the code a bit easier to understand, and I have also changed the code to use regular Lua string patterns instead of Scribunto's patterns for Unicode strings. The original code has test cases here.
-- gsplit: iterate over substrings in a string separated by a pattern
--
-- Parameters:
-- text (string) - the string to iterate over
-- pattern (string) - the separator pattern
-- plain (boolean) - if true (or truthy), pattern is interpreted as a plain
-- string, not a Lua pattern
--
-- Returns: iterator
--
-- Usage:
-- for substr in gsplit(text, pattern, plain) do
-- doSomething(substr)
-- end
local function gsplit(text, pattern, plain)
local splitStart, length = 1, #text
return function ()
if splitStart then
local sepStart, sepEnd = string.find(text, pattern, splitStart, plain)
local ret
if not sepStart then
ret = string.sub(text, splitStart)
splitStart = nil
elseif sepEnd < sepStart then
-- Empty separator!
ret = string.sub(text, splitStart, sepStart)
if sepStart < length then
splitStart = sepStart + 1
else
splitStart = nil
end
else
ret = sepStart > splitStart and string.sub(text, splitStart, sepStart - 1) or ''
splitStart = sepEnd + 1
end
return ret
end
end
end
-- split: split a string into substrings separated by a pattern.
--
-- Parameters:
-- text (string) - the string to iterate over
-- pattern (string) - the separator pattern
-- plain (boolean) - if true (or truthy), pattern is interpreted as a plain
-- string, not a Lua pattern
--
-- Returns: table (a sequence table containing the substrings)
local function split(text, pattern, plain)
local ret = {}
for match in gsplit(text, pattern, plain) do
table.insert(ret, match)
end
return ret
end
Some examples of the split function in use:
local function printSequence(t)
print(unpack(t))
end
printSequence(split('foo, bar,baz', ',%s*')) -- foo bar baz
printSequence(split('foo, bar,baz', ',%s*', true)) -- foo, bar,baz
printSequence(split('foo', '')) -- f o o
Upvotes: 11
Reputation: 151
Here is the function:
function split(pString, pPattern)
local Table = {} -- NOTE: use {n = 0} in Lua-5.0
local fpat = "(.-)" .. pPattern
local last_end = 1
local s, e, cap = pString:find(fpat, 1)
while s do
if s ~= 1 or cap ~= "" then
table.insert(Table,cap)
end
last_end = e+1
s, e, cap = pString:find(fpat, last_end)
end
if last_end <= #pString then
cap = pString:sub(last_end)
table.insert(Table, cap)
end
return Table
end
Call it like:
list=split(string_to_split,pattern_to_match)
e.g.:
list=split("1:2:3:4","\:")
For more go here:
http://lua-users.org/wiki/SplitJoin
Upvotes: 15
Reputation: 8041
Simply sitting on a delimiter
local str = 'one,two'
local regxEverythingExceptComma = '([^,]+)'
for x in string.gmatch(str, regxEverythingExceptComma) do
print(x)
end
Upvotes: 5
Reputation: 11596
Because there are more than one way to skin a cat, here's my approach:
Code:
#!/usr/bin/env lua
local content = [=[
Lorem ipsum dolor sit amet, consectetur adipisicing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna
aliqua. Ut enim ad minim veniam, quis nostrud exercitation
ullamco laboris nisi ut aliquip ex ea commodo consequat.
]=]
local function split(str, sep)
local result = {}
local regex = ("([^%s]+)"):format(sep)
for each in str:gmatch(regex) do
table.insert(result, each)
end
return result
end
local lines = split(content, "\n")
for _,line in ipairs(lines) do
print(line)
end
Output:
Lorem ipsum dolor sit amet, consectetur adipisicing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna
aliqua. Ut enim ad minim veniam, quis nostrud exercitation
ullamco laboris nisi ut aliquip ex ea commodo consequat.
Explanation:
The gmatch function works as an iterator, it fetches all the strings that match regex. The regex takes all characters until it finds a separator.
Upvotes: 10
Reputation: 701
I used the above examples to craft my own function. But the missing piece for me was automatically escaping magic characters.
Here is my contribution:
function split(text, delim)
-- returns an array of fields based on text and delimiter (one character only)
local result = {}
local magic = "().%+-*?[]^$"
if delim == nil then
delim = "%s"
elseif string.find(delim, magic, 1, true) then
-- escape magic
delim = "%"..delim
end
local pattern = "[^"..delim.."]+"
for w in string.gmatch(text, pattern) do
table.insert(result, w)
end
return result
end
Upvotes: 3
Reputation: 23357
I like this short solution
function split(s, delimiter)
result = {};
for match in (s..delimiter):gmatch("(.-)"..delimiter) do
table.insert(result, match);
end
return result;
end
Upvotes: 7
Reputation: 61
You can use this method:
function string:split(delimiter)
local result = { }
local from = 1
local delim_from, delim_to = string.find( self, delimiter, from )
while delim_from do
table.insert( result, string.sub( self, from , delim_from-1 ) )
from = delim_to + 1
delim_from, delim_to = string.find( self, delimiter, from )
end
table.insert( result, string.sub( self, from ) )
return result
end
delimiter = string.split(stringtodelimite,pattern)
Upvotes: 6
Reputation: 1125
If you just want to iterate over the tokens, this is pretty neat:
line = "one, two and 3!"
for token in string.gmatch(line, "[^%s]+") do
print(token)
end
Output:
one,
two
and
3!
Short explanation: the "[^%s]+" pattern matches to every non-empty string in between space characters.
Upvotes: 40
Reputation: 202715
Just as string.gmatch will find patterns in a string, this function will find the things between patterns:
function string:split(pat)
pat = pat or '%s+'
local st, g = 1, self:gmatch("()("..pat..")")
local function getter(segs, seps, sep, cap1, ...)
st = sep and seps + #sep
return self:sub(segs, (seps or 0) - 1), cap1 or sep, ...
end
return function() if st then return getter(st, g()) end end
end
By default it returns whatever is separated by whitespace.
Upvotes: 20
Reputation: 2753
If you are splitting a string in Lua, you should try the string.gmatch() or string.sub() methods. Use the string.sub() method if you know the index you wish to split the string at, or use the string.gmatch() if you will parse the string to find the location to split the string at.
Example using string.gmatch() from Lua 5.1 Reference Manual:
t = {}
s = "from=world, to=Lua"
for k, v in string.gmatch(s, "(%w+)=(%w+)") do
t[k] = v
end
Upvotes: 45
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