my @data = ...

xadd( \@data, "3.4", 1);

sub xadd
{
  my $data = shift;
  my $elem = shift;
  my $incr = shift || 1;

  for ( 0..$#{$data} )
  {
    $data->[1]->[$_] += $incr,
    $i = 1,
    last
      if $data->[0]->[$_] eq $elem;
  }
  
  unless ( $i )
  {
    push @{$data->[0]}, $elem;
    push @{$data->[1]}, $incr;
    $data->[2] = [ sort { $a <=> $b } @{$data->[1]};
  }

  # comment this line out if you don't 
  # need to re-sort the 3rd array
  $data->[2] = [ sort { $a <=> $b } @{$data->[1]};

}