while (<INPUTB>)
{
   my ($u, $superclass,$rel,$v) = (split)[0,1,2,3];
   my $conteggio=&calcolo($u,$v);
   
   print OUT "$u"."\t".$rel."\t".$v."\t".$conteggio."\n";
}

##</code><code>##

my $cur_superclass;
my @records;
while (<INPUTB>)
{
   my ($u, $superclass,$rel,$v) = (split)[0,1,2,3];
   $cur_superclass = $superclass if !defined($cur_superclass);
   if ($cur_superlclass ne $superclass) {
      my $conteggio=calcolo(\@records);
      print OUT "$u"."\t".$rel."\t".$v."\t".$conteggio."\n";
      @records = ();
   }
   push @records, [ $u, $superclass, $rel, $v ];
   $cur_superclass = $superclass;
}

##</code><code>##

sub calcolo {
    my $rRecs = shift;

    # Number of records
    my $found_recs = @{$rRecs};

    for my $rRec (@$rRecs) {
        # compute partial values
        my ($u, $superclass, $rel, $v) = @$rRec;
        ....
    }

    # combine partials
    return  $partials / $found_recs;  # or some such...
}