use warnings;
use strict;

use Data::Dumper;


my @accounts = ("A x1 B y1 C z1 D v1 E w1 F", 
                "A x2 B y2 C zzz2 D v2 E w2 F", 
                "A x3 B y3 C z3 D v3 E w3 F", 
                "A x4 B y4 C z4 D v4 E wwww4 F",
                "A x5 B y5 C z5 D v5 E w5 F", 
                "A x6 B y6 C z6 D v6 E    F");

my %fields = map { $_ => 1 } qw/A B C D E F/;

my $cur_field;
my %hash;

foreach ( @accounts ) {
    foreach ( split ) { 
        $cur_field = $_ if exists $fields{$_};
        push @{$hash{$cur_field}}, $_ 
            if $_ ne $cur_field;
    }
}

print Dumper \%hash;

__END__
$VAR1 = {
          'A' => [
                   'x1',
                   'x2',
                   'x3',
                   'x4',
                   'x5',
                   'x6'
                 ],
          'B' => [
                   'y1',
                   'y2',
                   'y3',
                   'y4',
                   'y5',
                   'y6'
                 ],
          'C' => [
                   'z1',
                   'zzz2',
                   'z3',
                   'z4',
                   'z5',
                   'z6'
                 ],
          'D' => [
                   'v1',
                   'v2',
                   'v3',
                   'v4',
                   'v5',
                   'v6'
                 ],
          'E' => [
                   'w1',
                   'w2',
                   'w3',
                   'wwww4',
                   'w5'
                 ]
        };