Following the hint in http://www.perlmonks.com/?node_id=564943,
I tried the following with map and grep:

use strict;
use Data::Dumper;

my ($hash, @array);
my @array = <DATA>;  


$hash ={ map 
            { chomp; my $key = (split(/\t/) )[0]; 
            $key => [ 
                    grep {
                            chomp; $_ 
                            if( (split(/\t/) )[0] =~/$key/) 
                        } @array 
                    ]  
            } @array 
        };

print Dumper(\%$hash);

__DATA__
1    2    a
1    13    w
1    20    c
2    1    b
2    40    n
3    30    a
[download]

Note: DATA should be tab delimited for this to work