From: Robert Klemme <bob.news@...>
Date: 2005-01-10T17:46:22+09:00
Subject: Re: brute force string search


"Robert Klemme" <bob.news@gmx.net> schrieb im Newsbeitrag
news:34es3pF48qpjkU1@individual.net...
>
> "Martin Pirker" <crf@sbox.tu-graz.ac.at> schrieb im Newsbeitrag
> news:41e1d123$0$11610$3b214f66@aconews.univie.ac.at...
> > Hi...
> >
> > given: String of several Mb
> > problem: find the lines in String containing "xyz"
> >
> >
> > Idea 1:
> > String.scan(/.*xyz.*/) -> ~10s runtime
>
> Did you try the anchored version?  Did it make a difference?
>
> >> s = "a\nbxyz\ncxyz\nd"
> => "a\nbxyz\ncxyz\nd"
> >> s.scan(/^.*xyz.*$/)
> => ["bxyz", "cxyz"]
>
> Did you try the block form, i.e.,
>
> s.scan(/^.*xyz.*$/) {|m| # work with m}
>
> > 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
> >
> >
> > C extension the only faster option left? :-)
>
> Im not sure whether you will gain much, because certain things will have
> to be done anyway: allocation of the result array, of the match strings
> and expansion of the result array.
>
> Kind regards
>
>     robert
>

Here are other options:

>> s.inject([]){|ar,x| (x.chomp! ; ar << x) if /xyz/ =~ x; ar}
=> ["bxyz", "cxyz"]
>> s.inject([]){|ar,x| (x.chomp! ; ar << x) if x.include? "xyz"; ar}
=> ["bxyz", "cxyz"]

Cheers

    robert