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package Array::Unique;

use 5.006;
use strict;
use warnings;
use Carp;

our $VERSION = '0.09';

# Strips out any duplicate values (leaves the first occurrence
# of every duplicated value and drops the later occurrences).
# Removes all undef values.
sub unique {
    my $self = shift; # self or class

    my %seen;
    my @unique = grep defined $_ && !$seen{$_}++, @_;
    # based on the Cookbook 1st edition and on suggestion by Jeff 'japhy' Pinyan
    # fixed by  Werner Weichselberger
}


sub TIEARRAY {
    my $class = shift;
    my $self = {
        array => [],
        hash => {},
        };
    bless $self, $class;
}


sub CLEAR     { 
    my $self = shift;
    $self->{array} = [];
    $self->{hash} = {};
}

sub EXTEND {}

sub STORE {
    my ($self, $index, $value) = @_;
    $self->SPLICE($index, 1, $value);
}



sub FETCHSIZE { 
    my $self = shift;
    return scalar @{$self->{array}};
}

sub FETCH { 
    my ($self, $index) = @_;
    ${$self->{array}}[$index];
}


sub STORESIZE { 
    my $self = shift;
    my $size = shift;

    # We cannot enlarge the array as the values would be undef

    # But we can make it smaller
#   if ($self->FETCHSIZE > $size) {
#   $self->{->_splice($size);
#    }

    $#{$self->{array}} = $size-1;
    return $size;
}

sub SPLICE {
    my $self = shift;
    my $offset = shift;
    my $length = shift;

lib/Array/Unique.pm  view on Meta::CPAN

=head1 NAME

Array::Unique - Tie-able array that allows only unique values

=head1 SYNOPSIS

 use Array::Unique;
 tie @a, 'Array::Unique';

 Now use @a as a regular array.

=head1 DESCRIPTION

This package lets you create an array which will allow
only one occurrence of any value.

In other words no matter how many times you put in 42
it will keep only the first occurrence and the rest will
be dropped.

You use the module via tie and once you tied your array to
this module it will behave correctly.

Uniqueness is checked with the 'eq' operator so 
among other things it is case sensitive.

As a side effect the module does not allow undef as a value in the array.

=head1 EXAMPLES

 use Array::Unique;
 tie @a, 'Array::Unique';

 @a = qw(a b c a d e f);
 push @a, qw(x b z);
 print "@a\n";          # a b c d e f x z

=head1 DISCUSSION

When you are collecting a list of items and you want 
to make sure there is only one occurrence of each item,
you have several option:


=over 4

=item 1) using an array and extracting the unique elements later

You might use a regular array to hold this unique set of values
and either remove duplicates on each update by that keeping the array
always unique or remove duplicates just before you want to use the 
uniqueness feature of the array. In either case you might run a 
function you call @a = unique_value(@a);

The problem with this approach is that you have to implement 
the unique_value function (see later) AND you have to make sure you 
don't forget to call it. I would say don't rely on remembering this.
 

There is good discussion about it in the 1st edition of the 
Perl Cookbook of O'Reilly. I have copied the solutions here, 
you can see further discussion in the book.

Extracting Unique Elements from a List (Section 4.6 in the Perl Cookbook 1st ed.)

# Straightforward

 %seen = ();
 @uniq = ();
 foreach $item (@list) [
     unless ($seen{$item}) {
       # if we get here we have not seen it before
       $seen{$item} = 1;
       push (@uniq, $item);
    }
 } 

# Faster

 %seen = ();
 foreach $item (@list) {
   push(@uniq, $item) unless $seen{$item}++;
 }

# Faster but different

 %seen;
 foreach $item (@list) {
   $seen{$item}++;
 }
 @uniq = keys %seen;

 # Faster and even more different
 %seen;
 @uniq = grep {! $seen{$_}++} @list;


=item 2) using a hash

Some people use the keys of a hash to keep the items and
put an arbitrary value as the values of the hash:

To build such a list:

 %unique = map { $_ => 1 } qw( one two one two three four! );

To print it:

 print join ", ", sort keys %unique;

To add values to it:

 $unique{$_}=1 foreach qw( one after the nine oh nine );

To remove values:

 delete @unique{ qw(oh nine) };

To check if a value is there:

 $unique{ $value };        # which is why I like to use "1" as my value

(thanks to Gaal Yahas for the above examples)