From: Stefan Lang <langstefan@...>
Date: 2005-01-11T01:51:27+09:00
Subject: Re: brute force string search

Michael C. Libby wrote:

> On Mon, 2005-01-10 at 09:51 +0900, Martin Pirker wrote:
>> Hi...
>> 
>> given: String of several Mb
>> problem: find the lines in String containing "xyz"
>> 
>> 
>> Idea 1:
>> String.scan(/.*xyz.*/) -> ~10s runtime
>> 
>> Idea 2:
>> String.grep(/.*xyz.*/) -> ~3s (but gives the \n too)
>> 
>> Idea 3:
>> loop String.index("xyz",lastmatch+3)
>> loop results array and grep in match area for line
>> -> 0,5s
> 
> Did you try something like this?
> 
> irb(main):003:0> big_string.each do |x| puts x if x=~/xyz/ end

Perhaps faster with: ... if x.include? "xyz"

> eeexyzfff
> qqqqxyzqqq
> => "abc\neeexyzfff\naadfwe\nqqqqxyzqqq\n"
> irb(main):004:0> big_string.split.grep(/xyz/)
> => ["eeexyzfff", "qqqqxyzqqq"]
> irb(main):005:0>
> 
> Intuitively it seems to me that wildcards (especially unanchored) in REs
> will slow them down.
> 
>  -Michael

-- 
Stefan