Set.pm

# Copyright Bill Allombert <ballombe@debian.org> 2001.
# Modifications copyright 2002 Julian Gilbey <jdg@debian.org>

# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.

package Devscripts::Set;

use strict;

BEGIN {
    use Exporter ();
    use vars     qw(@EXPORT @ISA %EXPORT_TAGS);
    @EXPORT      = qw(SetMinus SetInter SetUnion);
    @ISA         = qw(Exporter);
    %EXPORT_TAGS = ();
}

# Several routines to work with arrays whose elements are unique
# (here called sets)

=head1 NAME

Devscripts::Set - Functions for handling sets.

=head1 SYNOPSIS

use Devscripts::Set;

@set=ListToSet(@list);

@setdiff=SetMinus(\@set1,\@set2);

@setinter=SetInter(\@set1,\@set2);

@setunion=SetUnion(\@set1,\@set2);

=head1 DESCRIPTION

ListToSet: Make a set (array with duplicates removed) from a list of
items given by an array.

SetMinus, SetInter, SetUnion: Compute the set theoretic difference,
intersection, union of two sets given as arrays.

=cut

# Transforms a list to a set, removing duplicates
# input:  list
# output: set

sub ListToSet (@) {
    my %items;

    grep $items{$_}++, @_;

    return keys %items;
}

# Compute the set-theoretic difference of two sets.