in reply to Return reference to hash keys

First, you are reinventing the wheel: see uniq in List::MoreUtils and How do I compute the difference of two arrays? How do I compute the intersection of two arrays? in perlfaq4. But this, of course, does not answer your question.

keys returns a list, not an array, and so if you want to return an array reference you necessarily need to create a new array. You could reduce your character and line count by simply returning an anonymous array reference: 

sub unique {
  my @refs = @_;
  my %files = ();
  foreach my $ref (@refs) {
    $files{$_}++ foreach (@$ref);
  }
  return [keys %files];
}

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For more info, see Making References in perlref.

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Re^2: Return reference to hash keys
by miketosh (Acolyte) on Nov 30, 2010 at 20:24 UTC

    Thanks! That is exactly what I needed. I didn't know the difference between a LIST and an ARRAY. I guess I still need to learn about it, but your solution for an anonymous array reference is exactly what I was looking for.

    Thanks a million.

    Here is my final code, for what it is worth. Yes, I needed to reinvent the wheel for portability, since getting List::MoreUtils is not an option... 
    sub compare {
  my @refs = @_;
  my ($all, $inter, $diff);
  my %files;
  foreach my $ref (@refs) {
    foreach (@$ref) {
      $files{$_}++;
    }
  }
  $all = [ keys %files ];
  foreach my $e (@$all) {
    push @{ $files{$e} > 1 ? $inter : $diff }, $e;
  }
  return ($all, $inter, $diff);
}

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[reply]
[d/l]
      The difference between a list and an array is discussed a bit in perldata. The short, oversimplified version of it is that lists are values and arrays are variables.

      Regarding not using List::MoreUtils, Yes, even you can use CPAN should have an on-point discussion for consideration.

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