This is a great idea. In fact, its such a great idea that its been done many times before. :) You've definitely hit on a useful technique.

This is pretty similar to recipe 4.8 in the Perl Cookbook 1st edition. 

foreach $e (@a, @b) { $count{$e}++ }

foreach $e (keys %count) {
    push(@union, $e);
    if ($count{$e} == 2) {
        push @isect, $e;
    } else {
        push @diff, $e;
    }
}

[download]

Here's my implementation with each operation calculated separatly. 

use strict;
use warnings;

my @one = qw( 1 2 3 5 6 8 10 );
my @two = qw( 2 4 6 8 10 );
print "One = @one\n";
print "Two = @two\n";
print "\n";

my %union;
@union{@one, @two} = ();
my @union = sort keys %union;
print "Union = @union\n";

my (%one, %two);
@one{@one} = ();
@two{@two} = ();

my %intersection = map {
    exists $one{$_} && exists $two{$_} 
    ? ($_ => undef) 
    : ()
} @one, @two;
my @intersection = sort keys %intersection;
print "Intersection = @intersection\n";

my %one_minus_two = map {
    exists $two{$_} 
    ? () 
    : ($_ => undef)
} @one;
my @one_minus_two = sort keys %one_minus_two;
print "One - Two = @one_minus_two\n";

my %symdiff = map {
    1 == ( exists($one{$_}) + exists($two{$_}) )
    ? ($_ => undef)
    : ()
} @one, @two;
my @symdiff = sort keys %symdiff;

print "Symdiff = @symdiff\n";

[download]

If I was doing a whole lot of set manipulation I'd look for a library that provides a complete suite of set theoretic operations--like Set::Object or Set::Scalar. For simple uniqueness, I'd probably stick with List::MoreUtils--some of its other functions like 'any' and 'all' offer such great readability improvements to my code that I have come to rely on it.


TGI says moo

In reply to Re: Idiom: hashes as sets by TGI
in thread Idiom: hashes as sets by vrk

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