The data set seems small enough. You can store all the list data in a hash. Since the hash key is unique you won't hjave duplicate data when you get the keys. You can use the value field to store the number of times the data is found. 
use strict;
use warnings;

my @list_a = ( 'a'..'g');
my @list_b = ( 'A'..'C', 'a'..'c');

my %count;
$count{$_}++ foreach (@list_a, @list_b);

foreach (sort keys %count) {
  print "$_ appears $count{$_} time.\n" if $count{$_} == 1;
}

[download]

In reply to Re: Compare two index lists by monktim
in thread Compare two index lists by pdotcdot

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.