Interesting problem. Maybe you could do something with a hash for your keys? This doesn't completely match your spec, although it matches your example. Perhaps you can adapt this for your needs...

my %keys = (
    a=>1,
    e=>2,
    i=>3,
    o=>4,
    u=>5,
);
my @records = ();
push @records, '1|2|3|d|4';
push @records, '1|2|3|a|4';
push @records, '1|2|3|d|4';
push @records, '1|2|3|o|4';

my @final = ();
my @result = ();
my $re = '';
map {my @flds=split /\|/; push @{$final[$keys{$flds[3]}||0]},$_} @reco
+rds;

# note that entry 0 is where the unmatched elements wind up...
print map{ "@{ $final[$_] }\n" } grep defined $final[$_],1..$#final;
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Maps used only for their side effects are kinda wierd, though. I'd replace the map with a foreach(@records) block so it's clearer what you're doing.

foreach(@records)
{
    my @flds=split /\|/;
    push @{$final[$keys{$flds[3]}||0]},$_;
}
[download]