Perl_Series II

Hashes
A hash is an un-ordered group of KEY-VALUE pairs and keys are unique strings(duplication of keys are not allowed). The values are scalar and they can be either a number ,a string or a reference. These are also called as associative arrays.

Before using the hash we have to first declare it 

my %hash ;

As I said above duplication of keys are not allowed and this property can be used to list out the elements without any repetition. Let us consider a array of numbers with repetition.
@numbers =(0,2,3,4,1,4,2,2,3,5,5)

my @unique;

my %hashes;

my @numbers =(0,2,3,4,1,4,2,2,3,5,5);

foreach my $value (@numbers) {

  if (! $hashes{$value}) {    

push @unique, $value;   $hashes{$value} = 1; 

}}

print @unique;

output:023415