my $r = 44;
my $hash = $self->{'residues'}{$modelCount};
for my $key ( grep { /^\w$r$/ } keys %$hash ) {
    print $key."\n";
}

##</code><code>##

my $r = 44;
my $hash = $self->{'residues'}{$modelCount};
while( my ($key, $value) = each %$hash ) {
    next if $key =~ /^\w$r$/;
    print $key."\n";
}