counting number of string occurrences

Question

I'm trying to count the number of times that " --" occurs in a string.

So for instance, it occurs twice here 'a --b --c'

I tried the following, but it gives me 4 instead of 2, any idea why?

argv='a --b --c'
count = 0
for i in string.gfind(argv, " --") do
   count = count + 1
end
print(count)

Answer 1

you can actually do this as a one-liner using string.gsub:

local _, count = string.gsub(argv, " %-%-", "")
print(count)

no looping required!

Not recommended for large inputs, because the function returns the processed input to the _ variable, and will hold onto the memory until the variable is destroyed.

Answer 2

This snippet could be helpful, based on response of Mike Corcoran & optimisation suggestion of WD40

function count(base, pattern)
    return select(2, string.gsub(base, pattern, ""))
end

print(count('Hello World', 'l'))