NAME
Algorithm::Numerical::Shuffle - Shuffle a list.
SYNOPSIS
use Algorithm::Numerical::Shuffle qw /shuffle/;
@shuffled = shuffle (1, 2, 3, 4, 5, 6, 7);
$in_situ = [qw /one two three four five six/];
shuffle $in_situ;
DESCRIPTION
"shuffle" performs a one pass, fair shuffle on a list. If the list is
passed as a reference to an array, the shuffle is done in situ.
The subroutine returns the list in list context, and a reference to the
list in scalar context.
COMPLEXITY
The running time of the algorithm is linear in the size of the list. For
an in situ shuffle, the memory overhead is constant; otherwise, linear
extra memory is used.
LITERATURE
The algorithm used is discussed by Knuth [3]. It was first published by
Fisher and Yates [2], and later by Durstenfeld [1].
CAVEAT
Salfi [4] points to a big caveat. If the outcome of a random generator
is solely based on the value of the previous outcome, like a linear
congruential method, then the outcome of a shuffle depends on exactly
three things: the shuffling algorithm, the input and the seed of the
random generator. Hence, for a given list and a given algorithm, the
outcome of the shuffle is purely based on the seed. Many modern
computers have 32 bit random numbers, hence a 32 bit seed. Hence, there
are at most 2^32 possible shuffles of a list, foreach of the possible
algorithms. But for a list of n elements, there are n! possible
permutations. Which means that a shuffle of a list of 13 elements will
not generate certain permutations, as 13! > 2^32.
REFERENCES
[1] R. Durstenfeld: *CACM*, 7, 1964. pp 420.
[2] R. A. Fisher and F. Yates: *Statistical Tables*. London, 1938.
Example 12.
[3] D. E. Knuth: *The Art of Computer Programming*, Volume 2, Third
edition. Section 3.4.2, Algorithm P, pp 145. Reading:
Addison-Wesley, 1997. ISBN: 0-201-89684-2.
[4] R. Salfi: *COMPSTAT 1974*. Vienna: 1974, pp 28 - 35.
SEE ALSO
"List::Util" also has a "shuffle" function which uses a similar
algorithm. But since it's written in C, it's much faster. For all
practical purposes, "List::Util" supersedes this module. Unless you
really need in situ sorting.
DEVELOPMENT
The current sources of this module are found on github,
<git://github.com/Abigail/algorithm--numerical--shuffle.git>.
AUTHOR
Abigail <mailto:
[email protected]>.
COPYRIGHT and LICENSE
Copyright (C) 1998 - 2000, 2009 by Abigail.
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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