LUA count repeating characters in string

Question

I have a string "A001BBD0" and i want to know this info:

• 0 repeats 3 times
• B repeats 2 times

and that's it.

I found this pattern on web: "([a-zA-Z]).*(\1)" but it always returns nil for some reason

I guess i should split this string and check each symbol in several loops. I don't think this is a good idea (low performance)

i also found this topic but it doesn't give me any information

Answer 1

Creating a record for each alphanumeric char will give a more generic solution

local records = {} -- {['char'] = #number of occurances}
s = "A001BBD0"
for c in string.gmatch(s, "%w") do
    if records[c] then
        records[c] = records[c] + 1
    else
        records[c] = 1
    end
end

for k,v in pairs(records) do
    if(v > 1) then -- print repeated chars
        print(k,v)
    end
end
-- Output:
-- 0    3
-- B    2