use strict;
use warnings;
use Data::Dumper;

my %hash;
my @records;

while (<DATA>) {
    chomp;
    my ($id, $first, $second) = split /\s+/;
    my $record = [ $id, $first, $second ];

    # Build hashes indexed by first and second numbers
    push(@{$hash{first}{$first}}, $record);
    push(@{$hash{second}{$second}}, $record);

    # Build array of records
    push(@records, $record);
}

print "\%hash:\n";
print Dumper(\%hash);
print "\n\n";

print "\@pairs:\n";
print Dumper(\@records);
print "\n\n";

print "records with first number 6, from hash:\n";
foreach my $record (@{$hash{first}{6}}) {
    print "\t", join(',',@$record), "\n";
}

print "records with first number 6, from array:\n";
foreach my $record (grep { $_->[1] == 6 } @records) {
    print "\t", join(',',@$record), "\n";
}

__DATA__
1    1               1
2    1               2
3    2               3
4    2               4
5    3               5
6    3               6
7    4               7
8    4               6
9    5               8
10    5               9
11    6              10
12    6               9