Additionally, List::MoreUtils uniq() will maintain your list order. Using a temporary hash is tempting, but it will almost certainly change the order of elements.

And List::MoreUtils::uniq can be faster as it tries to load a library to implement its functionality via DynaLoader. If that fails it implements a plain perl way.

In my test (linux, perl 5.8.8 List::MoreUtils 0.21) the original List::MoreUtils::uniq is about 400% faster than my perl implementation.

If I rename the library, so List::MoreUtils must rely on its perl implementation, my solution is about 20% - 25% faster.

I don't want to argue against List::MoreUtils; but now I wonder about these two (perl) solutions:

# presented in perlfaq4 - How can I remove duplicate elements from a l
+ist or array?
sub my_uniq {
  my %h;
  grep { !$h{$_}++ } @_;
}

# vs.

# List::MoreUtils::uniq
sub LM_uniq {
  my %h;
  map { $h{$_}++ == 0 ? $_ : () } @_;
}
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I can't recognize an advantage in the usage of map and the ternary operator.

edit: text refined

Using the @ in front of a hash means you're doing a hash slice, which allows you to assign multiple values to multiple keys in one step. In this case, you're creating keys out of the values in @array, and assigning them all undef (since you've got an empty list on the right-hand side of the assignment.)

Then you extract all the keys from the hash using the keys function. Since making a duplicate hash key does not add a new key to a hash, this has the effect of removing all duplicates.

push(@newunique,grep {!$ss{$_}++} @unique);
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