Difference of Two Arrays Using Perl

I have two arrays. I need to check and see if the elements of one appear in the other one.

Is there a more efficient way to do it than nested loops? I have a few thousand elements in each and need to run the program frequently.

Solution 1:

Another way to do it is to use Array::Utils

use Array::Utils qw(:all);

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

# symmetric difference
my @diff = array_diff(@a, @b);

# intersection
my @isect = intersect(@a, @b);

# unique union
my @unique = unique(@a, @b);

# check if arrays contain same members
if ( !array_diff(@a, @b) ) {
        # do something
}

# get items from array @a that are not in array @b
my @minus = array_minus( @a, @b );

Solution 2:

perlfaq4 to the rescue:

How do I compute the difference of two arrays? How do I compute the intersection of two arrays?

Use a hash. Here's code to do both and more. It assumes that each element is unique in a given array:

   @union = @intersection = @difference = ();
    %count = ();
    foreach $element (@array1, @array2) { $count{$element}++ }
    foreach $element (keys %count) {
            push @union, $element;
            push @{ $count{$element} > 1 ? \@intersection : \@difference }, $element;
    }

If you properly declare your variables, the code looks more like the following:

my %count;
for my $element (@array1, @array2) { $count{$element}++ }

my ( @union, @intersection, @difference );
for my $element (keys %count) {
    push @union, $element;
    push @{ $count{$element} > 1 ? \@intersection : \@difference }, $element;
}