From: Charles Mills <cmills@...>
Date: 2005-01-10T15:16:22+09:00
Subject: Re: brute force string search

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
>
Try the StringScanner library.  It is very fast.
###
require 'strscan'

scanner = StringScanner.new(str, false)
match = scanner.scan(/.*xyz.*/)
###
you will have to change your regexp in order to skip lines not
containing 'xyz' since it always matches from the current position in
the string.
Docs:  http://i.loveruby.net/en/prog/strscan.html
If you just want to count the number of lines you could use the regexp
look ahead and look behind instead of '.*'.

>
> C extension the only faster option left? :-)
> 

It is an option, but it might not be much faster.

-Charlie