my @set = qw(a b c);

my %uniq;
my @comb = grep !$uniq{$_}++, map join(",",sort split(//,$_)), glob(("
+{".join(",",@set)."}") x @set);

print "$_\n" for @comb;

__END__
a,a,a
a,a,b
a,a,c
a,b,b
a,b,c
a,c,c
b,b,b
b,b,c
b,c,c
c,c,c

[download]

Update: here's a slightly modified version which can handle not just single letters items (which would have been a problem with the first version...) — pick a separator as appropriate. 

my @set = qw(foo bar baz);

# use glob to expand all permutations
my @perm = glob( join(",", ("{".join(",",@set)."}") x @set) );

print "Permutations:\n";
print "$_\n" for @perm;

# filter out duplicates
my %uniq;
my @comb = grep !$uniq{$_}++, map join(",",sort split(/,/,$_)), @perm;

print "Combinations:\n";
print "$_\n" for @comb;

[download]

In reply to Re: finding combinations and removing selective duplicates by almut
in thread finding combinations and removing selective duplicates by targetsmart

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