CODEWITHSUNDEEP
arraysperl
CrazyEd38239
CrazyEd38239

Reputation: 37

How to get an unique element from two arrays in Perl

I have tried to get a list of the unique elements in the first array. (AKA: the elements in the first array that are NOT in the second array.) However my script returns the number of unique elements not the info in each element.

As a newbie to Perl, I know there are many nuances to the language. I have not seen how I am getting a number instead of a list of elements. The only research I have seen is how to get a number of unique elements and apparently, I have discovered another way.

Any help is appreciated. Below is the code.

#!/usr/bin/perl

use strict;
use warnings;
use v5.10;

use XML:Simple;
use LWP::Simple;
use List::Compare;

my @upd = system ("perl test.pl | grep '*.x86_64.rpm'");
my @inst = system ("rpm -qa");

@inst = join( '.rpm', @inst);

my $ls = List::Compare->new( {lists=> [\@upd, \@inst]} );
my @list = $ls->get_unique;
@list = $ls->get_Lonly;

say "@list";

Upvotes: 2

Views: 315

Answers (2)

ingueni
ingueni

Reputation: 49

Iterate through the list and check each element against every in the second list, if its not in the entire second list push it (or do whatever) to a new array

#!/usr/bin/perl

use strict;
use warnings;
use v5.10;
my @upd = ('cat', 'dog','mouse', 'fatcatsrul');
my @inst = ('cat', 'dog', 'mouse');
my @unique_elements_in_upd;
foreach(@upd)
{
    my $key= $_;
    if(!($key ~~@inst))
    {
        push(@unique_elements_in_upd, $key);
        print $key . "\n";
    }
}

output: fatcatsrul

check out this http://perlmaven.com/smart-matching-in-perl-5.10

also check out this comparison How fast is Perl's smartmatch operator when searching for a scalar in an array?

Upvotes: -3

ikegami
ikegami

Reputation: 385546

@upd contains one element, the exit status of the shell that executed perl test.pl | grep '*.x86_64.rpm'. Similarly, @inst contains one element, the exit status of rpm. Perhaps you were trying to capture the output? Use backticks.

my @upd  = `perl test.pl | grep '*.x86_64.rpm'`;
chomp(@upd);

my @inst = `rpm -qa`;
chomp(@inst);

Also, the following is incorrect:

@inst = join( '.rpm', @inst);

It should be replaced with the following:

$_ .= '.rpm' for @inst;

Upvotes: 4

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