for my $i (0 .. @F-1) {

##</code><code>##

    @F1 = @F if !@F1;

##</code><code>##

while (<DATA>) {
    chomp;
    my @F = split '&';

##</code><code>##

#!/usr/bin/env perl -w
use v5.014;
my %seen;
my $count;
my @recs;
while (<DATA>) {
    chomp;
    my @F = split '&';
    $count //= @F;
    die "NF mismatch" if @F != $count;
    $seen{$_}++ for @F;
    push @recs, \@F;
}

for my $rec (@recs) {
    say join "\t",
        grep $seen{$_} != @recs, # Doesn't show up in every record
        @$rec
        ;
}



__DATA__
a=1&b=1&c=1&d=2&e=&f=3
a=1&b=2&c=3&d=2&e=&f=4
a=1&b=2&c=5&d=1&e=&f=5