Name
Math::Transform::List - Generate specified transformations of a list.
Synopsis
use Math::Transform::List;
transform {say "@_"} [qw(a b c)], [1..3];
# a b c
# b c a
# c b a
transform {say "@_"} [qw(a b c d)], [1..2], [3..4];
# a b c d
# b a c d
# a b d c
# b a d c
transform {say "@_"} [qw(a b c d)], [[1, 3], [2, 4]];
# a b c d
# c d a b
Description
Generate and process all the all the transformations of a list using the
standard Perl metaphor.
"transform()" returns the number of transformations in both scalar and
array context.
"transform()" is easy to use and fast. It is written in 100% Pure Perl.
Please note that the order in which the transformations are generated is
not guaranteed, so please do not rely on it.
The parameters to "transform()" are:
1: The code to be executed for each transformation.
2: A reference to the list to be transformed. This list is transformed
as specified by the transformations. Each transformation of the list is
handed to the code supplied in parameter 1 to be processed.
3: One or more transformations to be applied to the list. The
transformations are applied repeatedly in all orders until no new
transformations of the list are generated. Each new transformation of
the list is handed to the code supplied in parameter 1 for processing.
Transformations are represented as permutations in cyclic format based
from 1 not 0. Two representations can be used to specify
transformations.
3a: Single cycle.
[1,2,3]
The first element of the list will be replaced by the second, the second
by the third, and the third by the first.
3a: Multi cycle.
[[1,3], [2,4]]
The first element of the list will be replaced by the third and vice
versa, while simultaneously the second element is replaced by the fourth
and vice versa.
transform {say "@_"} [qw(a b c d)], [[1, 3], [2, 4]];
# a b c d
# c d a b
If you want to produce all possible transformations of a list you should
consider Math::Permute::List as it is faster and easier to use than the
equivalent:
transform {} [1..$n], [1,2], [1..$n];
Export
The "transform()" function is exported.
Installation
Standard Module::Build process for building and installing modules:
perl Build.PL
./Build
./Build test
./Build install
Or, if you're on a platform (like DOS or Windows) that doesn't require
the "./" notation, you can do this:
perl Build.PL
Build
Build test
Build install
Author
PhilipRBrenan@appaapps.com
http://www.appaapps.com
Acknowledgements
With much help and good natured advice from Philipp Rumpf to whom I am
indebted.
See Also
Math::Cartesian::Product
Math::Disarrange::List
Math::Permute::List
Math::Subsets::List
Copyright
Copyright (c) 2009 Philip R Brenan.
This module is free software. It may be used, redistributed and/or
modified under the same terms as Perl itself.