use strict; 
use warnings; 
use diagnostics; 
use Data::Dumper; 
my %hash; 
my @data = ("foo",1, "bar",2, "foo",3, "baz",4); 
while (my $key = shift @data) { 
    my $value = shift @data; 
    push @{$hash{$key}}, $value; # push the value on the array 
} 
print Dumper \%hash

##</code><code>##

$VAR1 = {
          'bar' => [
                     2
                   ],
          'baz' => [
                     4
                   ],
          'foo' => [
                     1,
                     3
                   ]
        };