use strict;
use Data::Dumper;

my %hash;
while(<DATA>)
{
	chomp;
    my $line = $_;
	my $key = (split/\t/, $line)[0];
	
	push @{ $hash{$key} }, $line;
	
}
print Dumper(\%hash);

__DATA__
1	a	101
1	b	110
2	c	201
3	d	301
3	e	310
3	f	320
4	g	401