Perl has multidimensional hashes. Just do the following

my %dates;
while ...
...
$dates{$owner}{$job_id}= DateCalc( $dates{$owner}{$job_id}, ...
...
foreach (keys %{$dates{$owner}}) ...
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This takes care of problems 1 and 3. To solve problem 2 you might store the results of the Datecalc into a different hash and use arrays to accumulate them, i.e. push @{$results{$owner}}, DateCalc...