Did you write any own code for this?

use Data::Dumper;
my %hash;
while (<>) {
 chomp;
 my ($what,$where) = split /\s+/,$_;
 exists $hash{$what} || $hash{$what} = [];
 push @{$hash{$what}},$where;
}
print Dumper %hash;
[download]

(untested).
See perlreftut for more.