Soundex Lua

local d, digits, alpha = '01230120022455012623010202', {}, string.byte("A")
string.gsub(d, ".", function(c)
    digits[string.char(alpha)] = c
    alpha = alpha + 1
end)

local function Soundex(w)
    local res = {}

    for c in string.gmatch(string.upper(w), ".") do
        local d = digits[c]
        if d then
            if #res==0 then
                res[1] =  c
            elseif #res==1 or d~= res[#res] then
                res[1+#res] = d
            end
        end
    end
    if #res == 0 then
        return '0000'
    else
        res = string.gsub(table.concat(res), "0", "")
        return string.sub(res .. '0000',1,4)
    end
end