NAME

Data::Graph::Util - Utilities related to graph data structure

VERSION

This document describes version 0.006 of Data::Graph::Util (from Perl distribution Data-Graph-Util), released on 2019-02-15.

SYNOPSIS

 use Data::Graph::Util qw(toposort is_cyclic is_acyclic);

 # return nodes that satisfy the following graph: a must come before b, b must
 # come before c & d, and d must come before c.

 my @sorted = toposort(
     { a=>["b"], b=>["c", "d"], d=>["c"] },
 ); # => ("a", "b", "d", "c")

 # sort specified nodes (2nd argument) using the graph. nodes not mentioned in
 # the graph will be put at the end. duplicates are not removed.

 my @sorted = toposort(
     { a=>["b"], b=>["c", "d"], d=>["c"] },
     ["e", "a", "b", "a"]
 ); # => ("a", "a", "b", "e")

 # check if a graph is cyclic

 say is_cyclic ({a=>["b"]}); # => 0
 say is_acyclic({a=>["b"]}); # => 1

 # check if a graph is acyclic (not cyclic)

 say is_cyclic ({a=>["b"], b=>["c"], c=>["a"]}); # => 1
 say is_acyclic({a=>["b"], b=>["c"], c=>["a"]}); # => 0

DESCRIPTION

Early release. More functions will be added later.

Keywords: topological ordering, dependency sorting, dependency ordering.

FUNCTIONS

None are exported by default, but they are exportable.

toposort

Usage:

 toposort(\%graph[ , \@nodes ]) => sorted list

Perform a topological sort on graph (currently using the Kahn algorithm). Will return the nodes of the graph sorted topologically. Will die if graph cannot be sorted, e.g. when graph is cyclic.

If \@nodes is specified, will instead return @nodes sorted according to the topological order. Duplicates are allowed and not removed. Nodes not mentioned in graph are also allowed and will be put at the end.

is_cyclic

Usage:

 is_cyclic(\%graph) => bool

Return true if graph contains at least one cycle. Currently implemented by attempting a topological sort on the graph. If it can't be performed, this means the graph contains cycle(s).

is_acyclic

Usage:

 is_acyclic(\%graph) => bool

Return true if graph is acyclic, i.e. contains no cycles. The opposite of "is_cyclic".

HOMEPAGE

Please visit the project's homepage at https://metacpan.org/release/Data-Graph-Util.

SOURCE

Source repository is at https://github.com/perlancar/perl-Data-Graph-Util.

BUGS

Please report any bugs or feature requests on the bugtracker website https://rt.cpan.org/Public/Dist/Display.html?Name=Data-Graph-Util

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

SEE ALSO

https://en.wikipedia.org/wiki/Graph_(abstract_data_type)

https://en.wikipedia.org/wiki/Topological_sorting#Kahn.27s_algorithm

Algorithm::Dependency can also do topological sorting, but it is more finicky with input: graph cannot be epmty and all nodes need to be specified.

Sort::Topological can also sort a DAG, but cannot handle cyclical graph. It also performs poorly and eats too much RAM on larger graphs.

See Bencher::Scenario::GraphTopologicalSortModules for benchmarks.

AUTHOR

perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2019, 2017, 2016 by perlancar@cpan.org.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.