my $in = [
  {c_id => 1,  r_to => 0, dept => 0, p_id => 1, comm => 'this',},
  {c_id => 3,  r_to => 1, dept => 1, p_id => 1, comm => 'the other',},
  {c_id => 5,  r_to => 1, dept => 1, p_id => 1, comm => 'else',},
  {c_id => 6,  r_to => 5, dept => 2, p_id => 1, comm => 'that',},
  {c_id => 7,  r_to => 6, dept => 3, p_id => 1, comm => 'moreover',},
  {c_id => 9,  r_to => 3, dept => 2, p_id => 1, comm => 'no way',},
  {c_id => 10, r_to => 9, dept => 3, p_id => 1, comm => 'give',}, 
];