How to remove spaces from a string in Lua? - lua

Question

I want to remove all spaces from a string in Lua. This is what I have tried:
string.gsub(str, "", "")
string.gsub(str, "% ", "")
string.gsub(str, "%s*", "")
This does not seem to work. How can I remove all of the spaces?

Answer 1

It works, you just have to assign the actual result/return value. Use one of the following variations:
str = str:gsub("%s+", "")
str = string.gsub(str, "%s+", "")
I use %s+ as there's no point in replacing an empty match (i.e. there's no space). This just doesn't make any sense, so I look for at least one space character (using the + quantifier).

Answer 2

You use the following function :
function all_trim(s)
return s:match"^%s*(.*)":match"(.-)%s*$"
end
Or shorter :
function all_trim(s)
return s:match( "^%s*(.-)%s*$" )
end
usage:
str=" aa "
print(all_trim(str) .. "e")
Output is:
aae

Answer 3

The fastest way is to use trim.so compiled from trim.c:
/* trim.c - based on http://lua-users.org/lists/lua-l/2009-12/msg00951.html
from Sean Conner */
#include <stddef.h>
#include <ctype.h>
#include <lua.h>
#include <lauxlib.h>
int trim(lua_State *L)
{
const char *front;
const char *end;
size_t size;
front = luaL_checklstring(L,1,&size);
end = &front[size - 1];
for ( ; size && isspace(*front) ; size-- , front++)
;
for ( ; size && isspace(*end) ; size-- , end--)
;
lua_pushlstring(L,front,(size_t)(end - front) + 1);
return 1;
}
int luaopen_trim(lua_State *L)
{
lua_register(L,"trim",trim);
return 0;
}
compile something like:
gcc -shared -fpic -O -I/usr/local/include/luajit-2.1 trim.c -o trim.so
More detailed (with comparison to the other methods): http://lua-users.org/wiki/StringTrim
Usage:
local trim15 = require("trim")--at begin of the file
local tr = trim(" a z z z z z ")--anywhere at code

Answer 4

For LuaJIT all methods from Lua wiki (except for, possibly, native C/C++) were awfully slow in my tests. This implementation showed the best performance:
function trim (str)
if str == '' then
return str
else
local startPos = 1
local endPos = #str
while (startPos < endPos and str:byte(startPos) <= 32) do
startPos = startPos + 1
end
if startPos >= endPos then
return ''
else
while (endPos > 0 and str:byte(endPos) <= 32) do
endPos = endPos - 1
end
return str:sub(startPos, endPos)
end
end
end -- .function trim

Answer 5

If anyone is looking to remove all spaces in a bunch of strings, and remove spaces in the middle of the string, this this works for me:
function noSpace(str)
local normalisedString = string.gsub(str, "%s+", "")
return normalisedString
end
test = "te st"
print(noSpace(test))
Might be that there is an easier way though, I'm no expert!