ow, O(N2) time!

If the items in @group1 and @group2 are strings or can be represented by an id, it can be done in O(N) time. 

my %seen;
my @all = grep !$seen{$_}++, @group1, @group2;

[download]

Update:

If the items in @group1 and @group2 can be compared, it can be done in O(N log2 N) time (although order is lost). 

my @all;
my @group1_s = sort compare_func @group1;
my @group2_s = sort compare_func @group2;
while (@group1_s && @group2_s) {
   my $cmp = compare_func($group1_s[0], $group2_s[0]);
   if    ($cmp < 0) { push(@all, shift(@group1_s)); }
   elsif ($cmp > 0) { push(@all, shift(@group2_s)); }
   else             { push(@all, scalar(shift(@group1_s), shift(@group
+2_s))); }
}
push(@all, @group1_s, @group2_s);

[download]

In reply to Re: Combining arrays with grep/unless? by ikegami
in thread Combining arrays with grep/unless? by mdunnbass

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