#!/usr/bin/perl -w
use strict;
my %idhash;
my @ids;
foreach (@id_list){
   #split up your input line into something useful
   @ids = split (/-->/,$_);
   # check to see if that date is already in your hash and if it is newer
   if(defined($idhash{$ids[1]}) &&
   $idhash{$ids[1]} >= $ids[2]){
      next
   }else{
      #populate your hash
      $idhash{$ids[1]} = $ids[2];
   }
}
#then print your dates from the hash using foreach key