Either scan your data or build a lookup table (see perlreftut and perldsc), as follows. Which one is better in terms of the speed/memory tradeoff depends on how big the tables are and how many lookups you are performing.

use warnings;
use strict;

my %barcode_hash = (
    1 => ['AGCTCGTTGTTCGATCCA','GAGAGATAGATGATAGTG','TTTT_CCCC',0],
    2 => ['AGCTCGTTGTTCGATCCA','GAGAGATAGATGATAGTG','TTTT_AAAA',0],
    3 => ['AGCTCGTTGTTCGATCCA','GAGAGATAGATGATAGTG','TTTT_BBBB',0],
    4 => ['AGCTCGTTGTTCGATCCA','GAGAGATAGATGATAGTG','TTTT_AAAA',0],
);
my $barcode_pair_35 = 'TTTT_AAAA';

for my $key (sort keys %barcode_hash) {
    print "Found at $key\n"
        if $barcode_hash{$key}[2] eq $barcode_pair_35;
}

# - OR -

my %lookup;
for my $key (sort keys %barcode_hash) {
    push @{ $lookup{ $barcode_hash{$key}[2] } }, $key;
}
print "Looked up at ".join(", ",@{$lookup{$barcode_pair_35}})."\n";

__END__

Found at 2
Found at 4
Looked up at 2, 4

[download]

Updated: Replaced the hashref $data with the hash %barcode_hash to bring the code into line with your examples.

In reply to Re: search for particular elements of hash with multiple values by haukex
in thread search for particular elements of hash with multiple values by pmpmmpmp

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.