How can I extract just the unique elements of an array? is very helpful if that's what I want to do. But I need a list of all the elements that are *not* unique. And I need each element in this output list to be, itself, unique, even if it occurs more than twice in the input list. And to make matters worse, I need to do this in a for loop where I do other operations on the input list, so that shifting off one element after another is not an option. What I have at present is
my @in = qw/
test
foo
test
bar
baz
foo
test
/;
my %multiples;
my %out;
for (@in) {
if ($multiples{$_} == 1) {
$out{$_} = 1;
}
$multiples{$_} = 1;
}
print "$_\n" for keys %out;
This does what I want, but seems clunky. Is there a cute idiom for this operation?
§ George Sherston
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