...
$data{$master_key} ||= []; # if we haven't seen $master_key yet, create a fresh array
my %this_set;
for my $col(1 .. $eSheet->{MaxCol})
{
# Some logging for debugging
if( !defined $eSheet->{Cells}[$row][$col]) {
    print "Row $row: skipping empty column $col\n";
    next;
};
my $key= $eSheet->{Cells}[0][$col]->Value;
my $value = $eSheet->{Cells}[$row][$col]->Value;
$this_set{$key}=$value;
}
}
# Store our found set for that ID:
push @{ $data{ $master_key }}, \%this_set;