my %strcmp;

# get the uniq list
open( DF, "logfile.log" );
while(<DF>) {
        chomp;
        $data{(split(" ",$_))[2]}++;
}
close(DF);

my @keys = sort {$data{$b}<=>$data{$a}} keys %data;
@keys = splice(@keys,0,4000);

open( OUT, ">temp.dat" );
foreach my $line ( @keys ) { print OUT "$line\n"; }
close( OUT );

# create the list of strings matching the patterns
open(IN, "$outputfile");
while(<IN>) {
        chomp();
        # matche data
        foreach my $regexp ( keys %regexp ) {
                $strcmp{$_} = $regexp{$regexp} if ( $_ =~ m/$regexp/ );
        }
}
close( IN );

# applie this to the logfile
open( IN, "logfile.log" );
open( OUT, ">logfile_parsed.log" );
while(<IN>) {
        chomp;
        my @cols = split(" ",$_);
        next if( exists $strcmp{$cols[2]} );
        print OUT "$_\n";
}
close( OUT );
close( IN );
move( "logfile_parsed.log", "logfile.log" );

# from here more or less the same as the first perl listing.