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my @rows = qw/ 1 2 3 4 1 2 /; # 1 & 2 are dups
my @non_dupe_rows = do { my %seen;grep !$seen{$_}++, @rows };
print "@non_dupe_rows\n";

1 2 3 4

my @rows = qw/ 1 2 3 4 1 2 /; # 1 & 2 are dups
my @non_dupe_rows = do {
...
    grep $seen{$_} == 1, keys %seen
};
print "@non_dupe_rows\n";