

 
Manual Reference Pages  SET::CROSSPRODUCT (3)
.ds Aq ’
NAME
Set::CrossProduct  work with the cross product of two or more sets
CONTENTS
SYNOPSIS
my $iterator = Set::CrossProduct>new( ARRAY_OF_ARRAYS );
# get the number of tuples
my $number_of_tuples = $iterator>cardinality;
# get the next tuple
my $tuple = $iterator>get;
# move back one position
my $tuple = $iterator>unget;
# get the next tuple without resetting
# the cursor (peek at it)
my $next_tuple = $iterator>next;
# get the previous tuple without resetting
# the cursor
my $last_tuple = $iterator>previous;
# get a random tuple
my $tuple = $iterator>random;
# in list context returns a list of all tuples
my @tuples = $iterator>combinations;
# in scalar context returns an array reference to all tuples
my $tuples = $iterator>combinations;
DESCRIPTION
Given sets S(1), S(2), ..., S(k), each of cardinality n(1), n(2), ..., n(k)
respectively, the cross product of the sets is the set CP of ordered
tuples such that { <s1, s2, ..., sk>  s1 => S(1), s2 => S(2), ....
sk => S(k). }
If you do not like that description, how about:
Create a list by taking one item from each array, and do that for all
possible ways that can be done, so that the first item in the list is
always from the first array, the second item from the second array,
and so on.
If you need to see it:
A => ( a, b, c )
B => ( 1, 2, 3 )
C => ( foo, bar )
The cross product of A and B and C, A x B x C, is the set of
tuples shown:
( a, 1, foo )
( a, 1, bar )
( a, 2, foo )
( a, 2, bar )
( a, 3, foo )
( a, 3, bar )
( b, 1, foo )
( b, 1, bar )
( b, 2, foo )
( b, 2, bar )
( b, 3, foo )
( b, 3, bar )
( c, 1, foo )
( c, 1, bar )
( c, 2, foo )
( c, 2, bar )
( c, 3, foo )
( c, 3, bar )
If one of the sets happens to be empty, the cross product is empty
too.
A => ( a, b, c )
B => ( )
In this case, A x B is the empty set, so you’ll get no tuples.
This module combines the arrays that give to it to create this
cross product, then allows you to access the elements of the
cross product in sequence, or to get all of the elements at
once. Be warned! The cardnality of the cross product, that is,
the number of elements in the cross product, is the product of
the cardinality of all of the sets.
The constructor, new, gives you an iterator that you can
use to move around the cross product. You can get the next
tuple, peek at the previous or next tuples, or get a random
tuple. If you were inclined, you could even get all of the
tuples at once, but that might be a very large list. This module
lets you handle the tuples one at a time.
I have found this module very useful for creating regression
tests. I identify all of the boundary conditions for all of
the code branches, then choose bracketing values for each of them.
With this module I take all of the values for each test and
create every possibility in the hopes of exercising all of the
code. Of course, your use is probably more interesting. :)
METHODS
new( ARRAY_REF_OF_ARRAY_REFS )
Given the array of arrays that represent some sets, return a
Set::CrossProduct instance that represents the cross product
of those sets.
The single argument is an array reference that has as its
elements other array references. The new method will
return undef in scalar context and the empty list in list
context if you give it something different.
You must have at least two sets, or the constructor will
fail.
Return the carnality of the cross product. This is the number
of tuples, which is the product of the number of elements in
each set.
Strict set theorists will realize that this isn’t necessarily
the real cardinality since some tuples may be indentical, making
the actual cardinality smaller.
Return the pointer to the first element of the cross product.
get()
Return the next tuple from the cross product, and move the position
to the tuple after it.
In list context, get returns the tuple as a list. In scalar context
get returns the tuple as an array reference.
If you have already gotten the last tuple in
the cross product, then get returns undef in scalar context and
the empty list in list context.
Pretend we did not get the tuple we just got. The next
time we get a tuple, we will get the same thing. You
can use this to peek at the next value and put it back
if you do not like it.
You can only do this for the previous tuple. unget
does not do multiple levels of unget.
Return the next tuple, but do not move the pointer. This
way you can look at the next value without affecting your
position in the cross product.
In list context, get returns the tuple as a list. In scalar context
get returns the tuple as an array reference.
For the last combination, next() returns undef.
Return the previous tuple, but do not move the pointer. This
way you can look at the last value without affecting your
position in the cross product.
In list context, get returns the tuple as a list. In scalar context
get returns the tuple as an array reference.
Without an argument, done returns true if there are no more
combinations to fetch with get. and returns false otherwise.
With an argument, it acts as if there are no more arguments to fetch, no
matter the value. If you want to start over, use reset_cursor instead.
Return a random tuple from the cross product.
In list context, get returns the tuple as a list. In scalar context
get returns the tuple as an array reference.
Returns a reference to an arrray that contains all of the tuples
of the cross product. This can be quite large, so you might
want to check the cardinality first.
In list context, get returns the tuple as a list. In scalar context
get returns the tuple as an array reference. However, you should
probably always use this in scalar context except for very low
cardnalities to avoid returning huge lists.
TO DO
* it would be nice to be able to name the sets, and then access
elements from a tuple by name, like
my $i = Set::CrossProduct>new( {
Apples => [ ... ],
Oranges => [ ... ],
}
);
my $tuple = $i>get;
my $apple = $tuple>Apples;
* I need to fix the cardinality method. it returns the total number
of possibly nonunique tuples.
BUGS
* none that i know about (yet)
SOURCE AVAILABILITY
This source is in Github:
http://github.com/briandfoy/SetCrossProduct
If, for some reason, I disappear from the world, one of the other
members of the project can shepherd this module appropriately.
AUTHOR
brian d foy, <bdfoy@cpan.org>
COPYRIGHT AND LICENSE
Copyright (c) 20012010 brian d foy. All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
perl v5.20.3  SET::CROSSPRODUCT (3)  20111128 
Visit the GSP FreeBSD Man Page Interface. Output converted with manServer 1.07. 