#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper qw(Dumper);
use List::Util 'sum';

open my $fh, '<', \<<EOF;
The	DT	the
International	NN	International
for	IN	for
well	NN	well
preparation	NN	preparation
preparation	NN	preparation
in	IN	in
conference	NN	conference
conference	NN	conference
conferences	NN	conference
good	VVG	good
EOF

my %hash;
while (<$fh>) {
	chomp;
	my ($tag1, $tag2, $tag3) = split /\t/;
	
	if ($tag2 =~/NN/) {
		$hash{$tag3}{$tag1}++;
	}
}
print Dumper \%hash;

for my $tag (keys %hash) {
	printf "%s freq: %d\n", $tag, sum values %{ $hash{$tag} };	
}