Here's a method I use. It may not be the most efficient or elegant, but it works.

Basically, I use a hash array to get a union of the array and the hash (it could just as easily be 2 hashes), while keeping track of where the data came from....

Note that I stuck in some dummy data....

use strict;

my @user = (1,3,5,7,9);

my %log = ( 1 => 'today',
            2 => 'today',
            3 => 'yesterday',
            4 => 'last week',
            5 => 'now' );

my %result;

foreach my $x (@user) {
  # Save the id ($x) in the result hash, save the location
  # of data as value, 'both' if $log{$x} exists, user if not
  $result{$x} = $log{$x} ? 'both' : 'user';
}

foreach my $y (keys %log) {
  # Save the id ($y) in the result hash, save the location
  # of data as value only if the id does not exist in result
  # hash yet
  $result{$y} = 'log' unless $result{$y};
}

foreach my $z (sort keys %result) {
  print "$z: $result{$z}\n";
}
[download]

Here are the results:

1: both
2: log
3: both
4: log
5: both
7: user
9: user
[download]

Hope this helps.

Brian