[users] Re: random lines

[Steven Smolinski <steven.smolinski@sympatico.ca>]

"Martin F. Krafft" <madduck@madduck.net> wrote:
> also sprach Thomas J. Hamman (on Sun, 01 Jul 2001 11:58:32AM -0400):
> > What exactly is this for?  You could use fortune and strfile.  Make
> > the text file with a % symbol between each selection, like this:
> 
> a list of albums that i have on mp3 format.        and
> the desire to have a script that plays albums randomly
>   -- not a random song off any album,
>      but a random album from beginning to end
> 
> the strfile method is plausible, but i'd much rather work with the
> file that i have rather than autogenerate another one. and the file i
> got doesn't have any %'s.

I found this beauty in perlfaq5:

       How do I select a random line from a file?

       Here's an algorithm from the Camel Book:

           srand;
           rand($.) < 1 && ($line = $_) while <>;

       This has a significant advantage in space over reading the
       whole file in.  A simple proof by induction is available
       upon request if you doubt the algorithm's correctness.

It is a sweet algorithm, and doesn't require you know the length of the
file in advance.  The random line is in $line after the loop exits.

Steve
-- 
Steven Smolinski => http://arbiter.ca/