Lua splitting a string without separators

Question

Is there an easy way to split a string like this:

M34a79 or M2ab943 or M4c4

into

M,34,a,79 or M,2,ab,943 or M,4,c,4

without any separators?

• lhf: Leave the question as originally asked and add the solution as an answer.

Answer 1

You can do it with a pair of gsub calls:

x = "M34a79 or M2ab943 or M4c4"
x, _ = x:gsub( "(%d)(%a)", "%1,%2" )
x, _ = x:gsub( "(%a)(%d)", "%1,%2" )
print( x )

M,34,a,79 or M,2,ab,943 or M,4,c,4

Might not work in all cases, but does work on your example.

• Lukas: Yes, it works! :) Is it possible to store each of these values in variables?
• Kogitsune: Would you want it to be a table of them, like { "M", "34", "a", "79" }, { "M", "2", "ab", "943" }, { "M", "4", "c", "4" } ?
• Yu Hao: You don't need the _, just x = x:gsub( "(%d)(%a)", "%1,%2" ) is enough.

Answer 2

If you don’t mind using the LPEG library:

local lpeg = require "lpeg"
local C, Ct, P, R = lpeg.C, lpeg.Ct, lpeg.P, lpeg.R
local lpegmatch = lpeg.match
local extract
do
 local digit = R"09"
 local lower = R"az"
 local comma = P","
 local space = P" "
 local schema = Ct( C(P"M")
 * (digit^1 / tonumber)
 * C(lower^1)
 * (digit^1 / tonumber))
 local extractor = Ct((schema + 1)^0)
 extract = function (str)
 return lpegmatch (extractor, str)
 end
end

This will match all sequences of characters of the input that consist of (in that order)

• the letter M,
• a sequence of 1 or more decimal digits,
• a sequence of 1 or more lowercase characters, and
• another sequence of 1 or more decimal digits.

When processing the input each match is put in a subtable, the digits are converted to Lua numbers on the fly. Since the question requested it, the leading M is included in the entries.

Usage example:

local data = extract [[M34a79 or M2ab943 or M4c4]]
for i = 1, #data do
 local elm = data[i]
 print (string.format ("[%d] = { [1] = %q, [2] = %d, [3] = %q, [4] = %d },",
 i, table.unpack (elm)))
end

Output:

[1] = { [1] = "M", [2] = 34, [3] = "a", [4] = 79 },
[2] = { [1] = "M", [2] = 2, [3] = "ab", [4] = 943 },
[3] = { [1] = "M", [2] = 4, [3] = "c", [4] = 4 },

Answer 3

Solution:

http://www.coronalabs.com/blog/2013/04/16/lua-string-magic/

function string:split( inSplitPattern, outResults )
 ...
end
function val(x)
 x = x:gsub( "(%d)(%a)", "%1,%2" )
 x = x:gsub( "(%a)(%d)", "%1,%2" )
 Table = string.split(x,",")
 for i = 1, #Table do
 print( Table[i] ) 
 end
end
val("M3a5") 

returns M 3 a 5