Array::Unique(3pm)

okay bestie, welcome to Array::Unique(3pm) — a User Contributed Perl Documentation page about a tie-able array that allows only unique values. it's giving “one of each, please” energy and honestly? iconic. let's get into it 💅✨

🌸 NAME 🌸

Array::Unique — a tie-able array that allows only unique values. no cap, that's the whole name. 👑

⭐ SYNOPSIS ⭐

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

Now use @a as a regular array. 🫶

🦋 DESCRIPTION 🦋

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

In other words, no matter how many times you put in 42, it keeps only the first occurrence and the rest will be dropped. not them being ignored 💀

You use the module via tie, and once you've tied your array to this module it will behave correctly. good behavior only. 🌈

Uniqueness is checked with the 'eq' operator, so among other things it is case sensitive. A and a are different girlies, iykyk.

side effect alert: the module does not allow undef as a value in the array. no ghosts allowed 🙈

🎀 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

💅 DISCUSSION 💅

When you're collecting a list of items and you want to make sure there's only one occurrence of each item, you have several options. several. options. 💅

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 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. literally do not. 😭

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;

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. okay hash girlies stand up 💅

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) 🫶

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 none 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. big mood 😭

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 might be interesting 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. main character energy 👑

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

Since writing this I am not sure if I really recommend its usage. I would say stick with the hash version and document that the variable is aggregating a unique list of values. fr fr. 💜

4) Using real SET

There are modules on CPAN that let you create and maintain SETs. I have not checked any of those but I guess they just as much of an overkill for this functionality as Unique::Array.

💀 BUGS 💀

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

@c = @a = qw(a b c a d e f b);

@c will contain the same as @a AND two undefs at the end because @c you get the same length as the right most list. yeah. bug. 💀

🌈 TODO 🌈

Test:

Change size of the array Elements with false values ('', '0', 0)

splice:

splice @a;
splice @a,  3;
splice @a, -3;
splice @a,  3,  5;
splice @a,  3, -5;
splice @a, -3,  5;
splice @a, -3, -5;
splice @a,  ?,  ?, @b;

Benchmark speed

Add faster functions that don't check uniqueness so if I know part of the data that comes from a unique 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@pti.co.il> 💖

🔥 LICENSE 🔥

Copyright (C) 2002-2008 Gabor Szabo <gabor@pti.co.il> All rights reserved. http://www.pti.co.il/

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. like none. at all. 🙈

🌟 CREDITS 🌟

Thanks for suggestions and bug reports to

• Szabo Balazs (dLux)
• Shlomo Yona
• Gaal Yahas
• Jeff 'japhy' Pinyan
• Werner Weichselberger

🎀 VERSION 🎀

Version: 0.08

Date: 2008 June 04

okay bestie, that's the whole page! this one came from perl v5.42.0 and was dated 2023-05-30, and it's still Array::Unique(3pm) at heart. mwah 💋✨