Dear Masters,
My code below, tries to group the 'error_rate' (second column of data) based on its corresponding tag (first column of data). The grouping is done using Hash Of Array (HoA). Later, I will process each of these groups with some functions (not shown here).

However I found that given a large dataset, HoA is not feasible.
Is there any better memory efficient alternative to hash of array to address the problem equivalently? 
use strict;
use Data::Dumper;
use Carp;

my %hold;

while ( <DATA> ) {
    chomp;
    next if (/^\#/);
    my @elem = split(/\t/,$_);

    # Keep in Hash of Array
    # HoA here consumes so much memory
    push @{$hold{$elem[0]}}, $elem[1];

}               

# is there a better way to keep/process the array
# other than HoA like %hold ?


foreach my $key ( sort keys %hold  ) {

    my @ary = @{$hold{$key}};

    # then I will process @ary for each key above
    print "$key\n";

}               


# in practice there are ~4-5Gb of such lines below

__DATA__
#Tags                                Error_Rate_In_ASCII
AATACGGCCACCCCCCCCCCCCCCGCCCCTCCCC    INILILFIIIIQNQQNQNLLKFKNCDHA?DAH
+HH
CTTTCCCTCCACGACGCTCTTCCGCTCTCATGAT    QQIQQQQQIQQQIQQLQNQNOPNKIHHHAHHA
+AA
TCCACTCTTTCCCTACACGACGCTCTTCCGATCT    QFQFQQQQQQQQQQQQIQLFNNPONHHHHHDH
+HH
TCCCCTCTTTCCCTACACGACGCTCTTCCGATCT    UIUIUUUUUUUUUULUUUIOUKUNULLLLKKL
+LK
TGATACGGCGACCACCGAGATCATCACACTTTCC    UUUUUUUUUUUUUQUUTUUUUULLUKRHPKIH
+HO
TGATACGGCGACCACCGAGATCTACACTCTTTCC    UOIUIUUUUUUUUIUUUOUOUUUUUKLLLLIK
+KL
TGATACGGCGACCACCGAGATCTACACTCTTTCC    UUUUMUUUUUUUUIUUIUUQUUUUUOOOOOOO
+OO
TGATACGGCGACCACCGAGATCTACACTCTTTCC    UUUUUUUUUUUUUUUUUTUUUUUUURRRRRMP
+PQ
TGATACGGCGACCACCGAGATCTACACTCTTTCC    UUUUUUUUUUUUUUUUUUUUUUTUURRPRRIM
+QQ
TGATACGGCGACCACCGAGCTCTACACTCTTTCC    UUQUUUUUUUMUUUUUUQUUUUUUUOOOOOIO
+OO
AATTCTGCGCCCCCCCCACTCAGCCCCCCTCCCC    LFNFQNQNFLQLIQQLIIQNOCIIIAAAAAHH
+HA
AGATACGGCCACCACCGAGATCTACACTCTCTCC    NFQNIQLFQIFNQNQQFQQNNKKINAHAHH?A
+HD
TGATACGGCGACCACCGCGATCTACACTCTCTCC    UUUUUUUUUUUUUUUUTLUUQUUCUPRRRRHR
+NQ
TGATCCGGCGACCCCCGAGCTCTACACTCTTTCC    QQQQIQQIQQQQQNQQQQQLOOKNPHHHHHHD
+HH
TGCTCCGGCGACCACCGAGATCTACACTCTTTCC    QQIQFQQNQQQQQIQQQLQLNOKIOHHHHHAD
+HH
TGCTCCGGCGACCACCGAGATCTACACTCTTTCC    UIOUOULOUUUUUOUUUOUUUUUUULLKLLIG
+LL
TGCTCCGGCGACCACCGAGATCTACACTCTTTCC    ULOUIUOUUUUUUUUUULUUUUUUULLLLLIG
+LL
GTCTCCTGCGACCCCCGAGCTCTACACTCTTTCC    QLLQIQIFQNQQQIQQNQNLOONNOHHHHHHH
+HH
TTCTCCTTCGACCACCGAGATCTACACTCTTTCC    QLNQIQLIQINQQQQQQLQQOPONOHHHHHHH
+HH
TTCTCCTTCGACCACCGAGATCTACACTCTTTCC    UOUUIUOIUILUUUUUULUUUUUUULLLLLKL
+LL

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---
neversaint and everlastingly indebted.......

In reply to Memory Efficient Alternatives to Hash of Array by neversaint

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