I don't see that happening. Perhaps I have missed something.

use strict;
use warnings;

use Data::Dumper;

my @keys = qw{a e i o u};

my @records = qw{
   1|2|3|d|4
   1|2|3|a|4
   1|2|3|d|4
   1|2|3|o|4};

my @result =
   map {
           my $key = $_;
           grep { m{^(?:\d\|){3}$key\|\d$} } @records
       }
   @keys;

my $dd = Data::Dumper->new([\@result], [qw{*result}]);
print $dd->Dumpxs();
[download]

produces

@result = (
            '1|2|3|a|4',
            '1|2|3|o|4'
          );
[download]

Cheers,

JohnGG