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)

In Lua 5.1 and up you need to use string.gmatch instead of string.gfind — Smile4ever, Jul 29 '15 at 19:13

Mike Corcoran · Answer 1 · 2018-03-28T18:10:02.567

38

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.

edited Mar 28 '18 at 18:10

answered Jun 22 '12 at 14:27

Mike Corcoran

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8

Instead of using a dummy variable, [select](https://www.lua.org/manual/5.3/manual.html#pdf-select) can discard the first returned value, the string with substitutions, which reduces the memory footprint. – WD40 Mar 23 '18 at 17:30

score 17 · Answer 2 · answered Jul 10 '18 at 02:11

17

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'))

answered Jul 10 '18 at 02:11

Abhishek Kumar

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score 12 · Accepted Answer · answered Jun 22 '12 at 07:59

12

The - character has special meaning in patterns, used for a non-greedy repetition.

You need to escape it, i.e. use the pattern " %-%-".

answered Jun 22 '12 at 07:59

interjay

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counting number of string occurrences

3 Answers3