The solution posted by dragonchild is close. It just doesn't account for the fact that @selected_data has duplicate items in it.

@selected_data = qw(13 76 90 13 77 100 76 300 13 65 400 74 89 34 65);
@all_data = qw(1 5 2 8 12 87 13 76 98 77 89 90 11 65 43 74 43 32 34 67
+);

my %all_hash; $all_hash{$_} = undef for @all_data;

my $total = scalar grep( exists $all_hash{ $_ }, @selected_data );
print "Count (kyle) -> $total\n";
[download]

Your rules for what you count are a little strange, but this produces the same result.

Update 1: No it doesn't! You caught me out with the duplication of value 43 in @all_data.

Is it any better?

C:\test>p1
use List::Util qw[ sum ];;

@selected_data = qw(13 76 90 13 77 100 76 300 13 65 400 74 89 34 65);
@all_data = qw(1 5 2 8 12 87 13 76 98 77 89 90 11 65 43 74 43 32 34 67
+);;

++$seen{ $_ } for @selected_data, @all_data;;

print sum map{ $_ > 1 ? $_ - 1 : () } values %seen;;
13
[download]

Update2: This is better.

@selected_data = qw(13 76 90 13 77 100 76 300 13 65 400 74 89 34 65);
@all_data = qw(1 5 2 8 12 87 13 76 98 77 89 90 11 65 43 74 43 32 34 67
+);

@seen{ @all_data } = ();;

exists $seen{ $_ } and $count++ for @selected_data;;

print $count;;
12
[download]

This doesn't work because the number 43 appears twice in @all_data but not at all in @selected_data. Your algorithm counts it as a match when it shouldn't be.

Yep. I noticed after I posted and then updated. I've also updated with a working solution.

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"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

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Thanks for your help.

my %x; $x{$_} = undef for @selected_data;
my %y; $y{$_} = undef for @all_data;
my $total;
foreach my $k ( keys %x ) {
    $total++ if exists $y{$k};
}
print "Count -> $total\n";
[download]

dragonchild,
that doesn't work.
The count return from the code is "8", which is not correct, but correct result is "12".

I would like to compare the elements in @selected_data with @all_data array, if elements from @selected_data array found in @all_data, then increment the count.
thanks