lua pattern matching: delimited captures

Question

I am trying to parse a string such as: &1 first &2 second &4 fourth \\, and from it to build a table

t = {1=first, 2=second, 4=fourth}

I'm not very experienced with regex in general so my naive try (disregarding the \\ and table parts for the moment) was

local s = [[&1 first &2 second &4 fourth \\]]

for k,v in string.gmatch(s, "&(%d+)(.-)&") do
    print("k = "..k..", v = "..v)
end

which gives only the first captured pair when I was expecting to see two captured pairs. I've done some reading and found the lpeg library, but it's massively unfamiliar to me. Is lpeg needed here? Could anyone explain my error?

Answer 1

1. &(%d+)(.-)& matches &1 first &
2. Leaving 2 second &4 fourth \\ to be matched on
3. Your pattern does not match any further items

Answer 2

If you know that the values are one word, this should work:

string.gmatch(s, "&(%d+)%s+([^%s&]+)")

Take "&", followed by 1 or more digits (captured), followed by one or more space and then one or more non-space, non-& characters (captured).