One way to handle this would be to put your data into a database and query it out. That can be useful especially if you have many many records or you have a data set that grows over time, and you don't want to build it repeatedly.

I'd probably represent your data with an array of hashes.

my @records = (
    { employee => 10001, form => 10, date => 20090101, },
    { employee => 10002, form => 10, date => 20080515, },
    { employee => 10003, form => 10, date => 20080323, },
);
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What's nice about this is that each hash can expand to have more fields as necessary. When you want to summarize by any given field, you can do this:

sub summarize_by {
    my $field_name = shift @_;

    my %out;
    for my $r ( @records ) {
        push @{ $out{$r->{$field_name}} }, $r;
    }
    return \%out;
}
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What you'd get from that is a hash of arrays of hashes. Each key of the top level hash is a unique value of the field you specified, and that hash's values are references to an array of records that had that key-value combination.