/ 
Array-Unique-0.02
River stage one • 2 direct dependents • 5 total dependents
/ Array::Unique

NAME

Array::Unique - Tieable array that allows only unique values

SYNOPSIS

use Array::Unique;
tie @a, Array::Unique;
or
tie @a, Array::Unique, 'Std';
or
tie @a, Array::Unique, 'IxHash';

Use @a as a regular arrray.

DESCRIPTION

This package supplies two different implementation of
the Unique Array tie construct.

In both cases you tie a regular array to this class and
use your array as you did earlier but now if try to add
a value to the array in any way ($a[3]='s'; or push or 
unshift or splice) which value was already an element 
of the array the array will discard one of the copies.

By this you have an array where the values are unique.

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

The two implementations are:
Std    - the Standard version and the
         Array::Unique::Std
IxHash - a version using the Tie::IxHash module of
         Gurusamy Sarathy
         Array::Unique::IxHash;

You can select which implementation you would like to
use by providing its name in the tie construct.
The default currently is the Standard implementation.

The main differences between the two implementations
are speed and memory usage. 
The Standard version uses about the same amount of space 
as a regular array but adding new values takes O(n) time 
so filling in an originally empty array will take O(n^2) time.

The IxHash implementation requires installing Tie::IxHash
uses about 4 times more space than a regular array but
it is should be faster than the the Standard implementation.

The module does not allow undef as a value in the array.

DISCUSSION

When you are collecting a list of items and you want 
to make sure there is only one occurence of each item,
you have several option:
1) using 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 = map { $_ => 1 }
       (keys %unique, 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 explanation)

There are three drawbacks I see:
1) You type more.
2) Your reader might not understand at first why did you use hash 
   and what will be the values.
3) You lose the order.

Usually non of them is critical but when I saw this the 10th time
in a code I had to understand with 0 documentation I got frustrated.
2) using array
Other people might use real arrays and on each update or
before they want to use the uniqueness feature of the array
they might run a function they call @a = unique_value(@);

This is also good but you have to implement the unique_value
function AND you have to make sure you don't forget to call it.
Something I have a tendency to do just before code release.
3) using Array::Unique
So I decided to write this module because I got frustrated
by my lack of understanding what's going on in that code
I mentioned.
In addition I thought it can a good game to write this and
then benchmark it.
Additionally it is nice to have your name displayed in 
bright lights all over CPAN ... or at least in a module.

Array::Unique lets you tie an array to hmmm, itself (?)
and makes sure the values of the array are always unique.

BUGS

I think you cannot use two different implementations
in the same script.

Cannot use negative indexes in Splice (?)

TODO

Benchmark speed

Add faster functions that don't check uniqueness so if I 
  know part of the data that comes from a uniques source then
  I can speed up the process,
  In short shoot myself in the leg.

Enable optional compare with other functions

Write even better implementations.

AUTHOR

Gabor Szabo <gabor@perl.org.il>

Copyright (C) 2002 Gabor Szabo <gabor@perl.org.il>
All rights reserved.

You may distribute under the terms of either the GNU 
General Public License or the Artistic License, as 
specified in the Perl README file.

No WARRANTY whatsoever.

SUPPORT

There is no official support for this package but
you can send bug reports directly to the author.

To get other support answers you should use either
the Hungarian Perl mailing list at perl@atom.hu
if you want to ask in Hungarian or the Israeli Perl 
mailing list at http://www.perl.org.il/ in English.

CREDITS

Thanks for suggestions and bug reports to 
Szabo Balazs (dLux)
Shlomo Yona
Gaal Yahas

VERSION

Version: 0.02      
Date:    2002.07.26