+---------------------------------------+
|            |   Event   | Date/Time 1  |
|            |    CNN    | Date/Time 2  |
|            |           | (etc)        |
|            +-----------+------------- |
|            |   Event   | Date/Time 1  |
|  unique    |    PHB    | Date/Time 2  |
|   unit #   |           | (etc)        |
|            +-----------+------------- |
|            |   Event   | Date/Time 1  |
|            |    CL     | Date/Time 2  |
|            |           | (etc)        |
|            +-----------+------------- |
|            |   Event   | Date/Time 1  |
|            |   SWAP    | Date/Time 2  |
|            |           | (etc)        |
+------------+-----------+--------------+
|            |   Event   | Date/Time 1  |
|            |    CNN    | Date/Time 2  |
|            |           | (etc)        |
|            +-----------+------------- |
| another    |   Event   | Date/Time 1  |
|  unique    |    PHB    | Date/Time 2  |
|  unit #    |           | (etc)        |
|            +-----------+------------- |
|            |   Event   | Date/Time 1  |
|            |    CL     | Date/Time 2  |
|            |           | (etc)        |
|            +-----------+------------- |
|            |   Event   | Date/Time 1  |
|            |   SWAP    | Date/Time 2  |
|            |           | (etc)        |
+---------------------------------------+

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

use vars
  qw(%HoH $field $unitNum $timestmp %hash $key);

# seed the hash with some data
%HoH = (
    8675309121 => {
            SWAPS => ["11/20/2009 12:43:00"],
    },
    5432129876 => {
            CNM => [ "11/20/2009 00:00:00" ],
            PHB => [ "11/20/2009 00:01:00", "11/20/2009 00:02:00" ],
    },
);
print Dumper( %HoH );

# reads sample data
while(<DATA>){
  # get a line of data
  chomp;
  my ($unit_num, $event_nm, $event_date) = split(/,/);

  %hash = (
             $unit_num => {
                $event_nm => [ $event_date ],
   },
  );

  @HoH{keys %hash} = values %hash 
}

print Dumper( %HoH );

__END__
1234567890,CNN,11/20/2009 00:01:00
1234567890,PHB,11/20/2009 00:01:02
8887776543,CL,11/20/2009 11:09:00