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Array::Unique - Tieable array that allows only unique values |
Array::Unique - Tieable array that allows only unique values
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.
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.
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
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:
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.
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.
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.
I think you cannot use two different implementations in the same script.
Cannot use negative indexes in Splice (?)
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.
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.
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.
Thanks for suggestions and bug reports to Szabo Balazs (dLux) Shlomo Yona Gaal Yahas
Version: 0.03 Date: 2002.07.27
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Array::Unique - Tieable array that allows only unique values |