array(10) {
  [0]=>
  object(stdClass)#37 (6) {
    ["id"]=>
    string(5) "31739"
    ["pro_title"]=>
    string(48) "Блуза с декором из пайеток"
    ["price"]=>
    string(9) "154100.00"
    ["parent_id"]=>
    string(5) "31739"
    ["photo_id"]=>
    string(6) "116489"
    ["value"]=>
    string(7) "Rodarte"
  }
  [1]=>
  object(stdClass)#38 (6) {
    ["id"]=>
    string(5) "31739"
    ["pro_title"]=>
    string(48) "Блуза с декором из пайеток"
    ["price"]=>
    string(9) "154100.00"
    ["parent_id"]=>
    string(5) "31739"
    ["photo_id"]=>
    string(6) "116489"
    ["value"]=>
    string(7) "Rodarte"
  }
  [2]=>
  object(stdClass)#39 (6) {
    ["id"]=>
    string(5) "31739"
    ["pro_title"]=>
    string(48) "Блуза с декором из пайеток"
    ["price"]=>
    string(9) "154100.00"
    ["parent_id"]=>
    string(5) "31739"
    ["photo_id"]=>
    string(6) "116489"
    ["value"]=>
    string(7) "Rodarte"
  }
  [3]=>
  object(stdClass)#40 (6) {
    ["id"]=>
    string(5) "31762"
    ["pro_title"]=>
    string(30) "Свитер из шерсти"
    ["price"]=>
    string(8) "39370.00"
    ["parent_id"]=>
    string(5) "31762"
    ["photo_id"]=>
    string(6) "116609"
    ["value"]=>
    string(5) "MONSE"
  }
  [4]=>
  object(stdClass)#41 (6) {
    ["id"]=>
    string(5) "31762"
    ["pro_title"]=>
    string(30) "Свитер из шерсти"
    ["price"]=>
    string(8) "39370.00"
    ["parent_id"]=>
    string(5) "31762"
    ["photo_id"]=>
    string(6) "116609"
    ["value"]=>
    string(5) "MONSE"
  }
  [5]=>
  object(stdClass)#42 (6) {
    ["id"]=>
    string(5) "31762"
    ["pro_title"]=>
    string(30) "Свитер из шерсти"
    ["price"]=>
    string(8) "39370.00"
    ["parent_id"]=>
    string(5) "31762"
    ["photo_id"]=>
    string(6) "116609"
    ["value"]=>
    string(5) "MONSE"
  }
  [6]=>
  object(stdClass)#43 (6) {
    ["id"]=>
    string(5) "31762"
    ["pro_title"]=>
    string(30) "Свитер из шерсти"
    ["price"]=>
    string(8) "39370.00"
    ["parent_id"]=>
    string(5) "31762"
    ["photo_id"]=>
    string(6) "116609"
    ["value"]=>
    string(5) "MONSE"
  }
  [7]=>
  object(stdClass)#44 (6) {
    ["id"]=>
    string(5) "31765"
    ["pro_title"]=>
    string(25) "Серьги Gold Baroque"
    ["price"]=>
    string(8) "50710.00"
    ["parent_id"]=>
    string(5) "31765"
    ["photo_id"]=>
    string(6) "116492"
    ["value"]=>
    string(7) "Rodarte"
  }
  [8]=>
  object(stdClass)#45 (6) {
    ["id"]=>
    string(5) "31768"
    ["pro_title"]=>
    string(40) "Топ из вискозы и шелка"
    ["price"]=>
    string(8) "90970.00"
    ["parent_id"]=>
    string(5) "31768"
    ["photo_id"]=>
    string(6) "116490"
    ["value"]=>
    string(7) "Rodarte"
  }
  [9]=>
  object(stdClass)#46 (6) {
    ["id"]=>
    string(5) "31768"
    ["pro_title"]=>
    string(40) "Топ из вискозы и шелка"
    ["price"]=>
    string(8) "90970.00"
    ["parent_id"]=>
    string(5) "31768"
    ["photo_id"]=>
    string(6) "116490"
    ["value"]=>
    string(7) "Rodarte"
  }
}

$result = [];
foreach($data as $o) {
   $result[$o->parent_id] = $o;
}

//$result = array_values($result);
print_r($result);

$data = [......];
usort($data, function($a, $b) {
  if ($a->parent_id < $b->parent_id)
    return -1;
  else if ($a->parent_id == $b->parent_id)
    return 0;
  else
    return 1;
});
$new_data = array_filter(
  $data,
  function($val, $key) {
    return ($key == 0) || ($data[$key - 1]->partent_id != $val->parent_id);
  },
  ARRAY_FILTER_USE_BOTH
);

$data = [..........];
$counts = [];
foreach ($data as $val) {
  if (!isset($counts[$val->parent_id])
    $counts[$val->parent_id] = 0;
  else
    $counts[$val->parent_id]++;
};
$new_data = array_filter(
  $data,
  function($val, $key) {
    if ($counts[$val->parent_id] === 0) {
      return true;
    $counts[$val->parent_id]--;
    return false;
  },
  ARRAY_FILTER_USE_BOTH
);