Can this program be golfed any more?

On the stackexchange code golf website there was a topic called "stretching words" and here is the basic concept:
Write a program or function that duplicates letters in a word, so that all the duplicated letters arranged in order would form the input array.
For example:
Input: abcdefghi, abc
Output: aabbccdefghi

Here is my shot at it in lua (76 bytes):

function f(x,y)for i=1,#x do g=y:sub(i,i);x=x:gsub(g,g..g,1)end print(x)end

My question is, can this code be golfed down anymore/is there a different way to approach this that is shorter?
Thanks!

How about this? That's 51 bytes:

function f(a,b)print(a:gsub("["..b.."]","%1%1"))end

Returns the correct string, but also returns an extra int. I'm pretty sure that isn't allowed

Well, that's the return of gsub. If you run this

function f(a,b)return a:gsub("["..b.."]","%1%1")end

local str = f( "abcdef", "ab" )
print( str )

It'll just print 'aabbcdef'. So that's a property of print.
However if you only want one return value, that's still 58 bytes

function f(a,b)print(({a:gsub("["..b.."]","%1%1")})[1])end

or with a return ( 57 bytes ):

function f(a,b)return({a:gsub("["..b.."]","%1%1")})[1]end

function f(a,b)print((a:gsub("["..b.."]","%1%1")))end

Note extra brackets.

wieselkatze, on 23 June 2015 - 05:25 PM said:

How about this? That's 51 bytes:

function f(a,b)print(a:gsub("["..b.."]","%1%1"))end

Untested but this should work

function f(a,b)print(a:gsub("["..b.."]","%1%1")[1])end[\code]
Since it'll only take the first return from gsub rather than gsub plus the number if string cut into

SquidDev, on 23 June 2015 - 06:09 PM said:

function f(a,b)print((a:gsub("["..b.."]","%1%1")))end

Note extra brackets.

Didn't know that property of brackets yet - interesting.

jerimo, on 23 June 2015 - 06:45 PM said:

Untested but this should work

function f(a,b)print(a:gsub("["..b.."]","%1%1")[1])end

Since it'll only take the first return from gsub rather than gsub plus the number if string cut into

Won't actually work - I already posted the proper way:

function f(a,b)print(({a:gsub("["..b.."]","%1%1")})[1])end

wieselkatze, on 23 June 2015 - 06:51 PM said:

SquidDev, on 23 June 2015 - 06:09 PM said:

function f(a,b)print((a:gsub("["..b.."]","%1%1")))end

Note extra brackets.

Didn't know that property of brackets yet - interesting.

jerimo, on 23 June 2015 - 06:45 PM said:

Untested but this should work

function f(a,b)print(a:gsub("["..b.."]","%1%1")[1])end

Since it'll only take the first return from gsub rather than gsub plus the number if string cut into

Won't actually work - I already posted the proper way:

function f(a,b)print(({a:gsub("["..b.."]","%1%1")})[1])end

Didn't think the extra parentheses and braces were needed, good to know!