Generating random strings

Question

I've created the following string manipulation function for randomizing my passed string in Lua:

require "string" require "math" math.randomseed( os.time() ) function string.random( self ) local tTemporary, tNew = {}, {} if not self or self:len() < 5 then return nil end self:gsub( "%a", function( cChar ) table.insert( tTemporary, cChar ) end ) for i = 1, #tTemporary, 1 do local iRandom = math.random(1, #tTemporary) tNew[i] = tTemporary[iRandom] table.remove( tTemporary, iRandom ) end return table.concat(tNew, " ") end 

Can this be optimized/more-randomised?

Answer 1

A couple of points to consider:

• Calling your function shuffle instead of random would be a better name since that's really what it's doing.
• The extra intermediate tables aren't really necessary to perform the shuffle. A single table is enough and you can perform the shuffle in-place right on that table.
• Consider a better separation between the process of shuffling and how the input is stored. For example, if you have your shuffle function take a table instead then that function can be reused on any kind of data and not just strings.
• I would do away with the Hungarian notation and just drop the type prefix on the variable names. Remember Lua variables themselves doesn't have a type. If you later change what that variable refers to then the Hungarian notation becomes misleading.

So I would refactor your original code into two functions. Here's one possibility:

function shuffle(self) if type(self) ~= 'table' then return nil end for i = #self, 2, -1 do local randi = math.random(i) self[i], self[randi] = self[randi], self[i] end return self end function shuffle_words(str) local strtable = {} for each in str:gmatch("%a+") do table.insert(strtable, each) end return table.concat(shuffle(strtable), ' ') end