data structures - How can I maintain the order of keys I add to a Perl hash?

Question

How can I maintain the order of actual list after counting its occurrence using a hash in the following program? For example, <DATA> are

a
b
e
a
c 
d 
a
c
d
b
etc.

Using hash, i counted the occurrence of each element.

and what i want is:

a  3
b  2
e  1
c  2
d  2

but the following program shows me otherwise.

my (%count, $line, @array_1, @array_2);
while ($line = <DATA>) {
    $count{$line}++ if ( $line =~ /S/ );
}
@array_1 = keys(%count);
@array_2 = values(%count);
for(my $i=0; $i<$#array_1; $i++)
{
   print "$array_1[$i] $array_2[$i]";
}

Answer 1

Hashes are not ordered, but as usual, CPAN offers a solution: Tie::IxHash

use Tie::IxHash;
my %count;
tie %count, 'Tie::IxHash';

while ($line = <DATA>) {
$count{$line}++ if ( $line =~ /S/ );
}

while( my( $key, $value)= each %count) {
    print "$key $value"; 
}