Perhaps you can adapt something along the lines of this ;

# input
#12/30/02 , 2584311 , 12, etc
#12/29/02 , 2584311 , 12, etc

use strict;
use warnings;

open (IN,"in.txt") or die "in.txt : $!";
my %data=();
my %count=();
while (<IN>){
  my ($date,@f) = split ',',$_;
  $data{$f[0]} = join ',',@f;
  ++$count{$f[0]};
}

open (OUT,">out.txt") or die "out.txt : $!";
foreach (sort keys %data){
  print OUT "$count{$_} : $data{$_}";  
}
[download]

poj