CODEWITHSUNDEEP
stringloopsluafind
Novarender
Novarender

Reputation: 57

Finding all instances of a string within a string

What is a way that I can find (and loop through) all instances of a string within another string in lua? For example, if I have the string

"honewaidoneaeifjoneaowieone"

And I want to loop through all instances (and by this, I mean indexes) of "one" within that string, well, I can see that it appears four times, but I have no clue how to actually find them. I know that string.find() can find the first instance, but that doesn't help me very much.

Upvotes: 3

Views: 2327

Answers (2)

lhf
lhf

Reputation: 72422

You can tell string.find where to start the search:

s="honewaidoneaeifjoneaowieone"
p="one"
b=1
while true do
    local x,y=string.find(s,p,b,true)
    if x==nil then break end
    print(x)
    b=y+1
end

This code starts each search after the end of the previous match, that is, it finds only non-overlapping occurrences of a string. If you want to find overlapping occurrences of a string, use b=x+1 instead.

Upvotes: 3

DarkWiiPlayer
DarkWiiPlayer

Reputation: 7064

local str = "honewaidoneaeifjoneaowieone"

-- This one only gives you the substring;
-- it doesn't tell you where it starts or ends
for substring in str:gmatch 'one' do
   print(substring)
end

-- This loop tells you where the substrings
-- start and end. You can use these values in
-- string.find to get the matched string.
local first, last = 0
while true do
   first, last = str:find("one", first+1)
   if not first then break end
   print(str:sub(first, last), first, last)
end

-- Same as above, but as a recursive function
-- that takes a callback and calls it on the
-- result so it can be reused more easily
local function find(str, substr, callback, init)
   init = init or 1
   local first, last = str:find(substr, init)
   if first then
       callback(str, first, last)
       return find(str, substr, callback, last+1)
   end
end

find(str, 'one', print)

Upvotes: 2

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