Assuming each line of your data is in @data_241 and NEW is the file handle you want to write to: 
my %latest;
foreach my $line (@data_241) {
  # split line
  my ($id, $date) = split(/\s+/, $line);
  if (! exists($latest{$id}) {
    # place in hash if not seen before
    $latest{$id} = $date;
  } else {
    # place in hash if date is greater than the one in hash
    $latest{$id} = $date if 
        substr($date,4,4).substr($date,0,4) ge
        substr($latest{$id},4,4).substr($latest{$id},0,4);
  }
}

foreach my $key (sort keys %latest) {
  # print out the latest values
  print NEW "$key\t$latest{$key}\n";
}

[download]
-imran

In reply to Re: Comparing rows keeping latest by CountOrlok
in thread Comparing rows keeping latest by Anonymous Monk

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