Beefy Boxes and Bandwidth Generously Provided by pair Networks
We don't bite newbies here... much

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
Sorry if I was unclear. The requirements are not mutually exclusive, I just need different types of "random" numbers at different places in the code. The shuffling subroutine needs to use a deterministic sequence of pseudo random (not truly random) numbers that are repeatable given the same seed. Other code outside the shuffle algorithm may eventually need to use random numbers based on rand() that are not repeatable like those used in the shuffle algorithm. Since this is a rather large persistent (mod_perl) application, it is difficult to foresee where rand() will be used in other code outside the shuffle subroutine, so I would like to avoid "tainting" it with a deterministic seed, or at least clean up afterwards by using a good seed.

What I am writing is a shuffle that can be seeded to always produce exactly one permutation per seed, but that when run with different seeds (seeds that are sequential integers, with some gaps) will produce a set of permutations that are reasonably uniformly distributed. I.e., if I sort the array qw(a b c d) 2400 times using 2400 different seeds, I should expect to see each of the 24 possible permutations about 100 times (plus/minus some tolerance).

Thanks to input from dws above, here is the code I wound up using, which meets my requirements and avoids altering the seed used by rand().

use Math::Random::MT (); sub shuffle { my $self = shift; my $seed = shift; my $array = $self; # ||rand() in case no seed passed to shuffle algorithm my $mt = Math::Random::MT->new( $seed || rand ); my $i; for($i = @$array; --$i; ) { my $j = int( $mt->rand($i + 1) ); @$array[$i, $j] = @$array[$j, $i]; } }
Thank you all for the replies.

In reply to Re: Re: Generating Repeatable Pseudorandom Sequences by mp
in thread Generating Repeatable Pseudorandom Sequences by mp

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.
Log In?

What's my password?
Create A New User
Domain Nodelet?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others rifling through the Monastery: (5)
As of 2023-01-27 17:56 GMT
Find Nodes?
    Voting Booth?

    No recent polls found