use strict;
use warnings;

use 5.10.1;

my $filter_clean = 'GAV18';

my %filter_map = (
    A => 2,
    B => 2,
    C => 2,
    D => 3,
    E => 3,
    F => 3,
    G => 4,
    H => 4,
    I => 4,
    J => 5,
    K => 5,
    L => 5,
    M => 6,
    N => 6,
    O => 6,
    P => 7,
    Q => 7,
    R => 7,
    S => 7,
    T => 8,
    U => 8,
    V => 8,
    W => 9,
    X => 9,
    Y => 9,
    Z => 9,
);

# 1st version

my $filter = q{};
if ($filter_clean) {

    my @filter_split = split //, $filter_clean;

    for my $fc (@filter_split) {
        if ( $fc =~ /\d/ ) {
            $filter .= $fc;
        }
        else {
            $filter .= $filter_map{ uc $fc };
        }
    }
}

say $filter;


# 2nd version. Why would I use below (when it's working right, that is
+) over above?

$filter .= map { $filter_map{ uc $_ } }
  grep { !/\d/ and $filter_clean } split//, $filter_clean;

say $filter;
[ghenry@linux]$ perl t/map.pl 
42818
428183
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