foreach ($form_state->getValues(['mytable','rows']) as $tablerow) {

$tablerow['label']

foreach ($entities as $id => $entity) {
    // TableDrag: Mark the table row as draggable.
    $form['mytable'][$id]['#attributes']['class'][] = 'draggable';
    // TableDrag: Sort the table row according to its existing/configured weight.
    $form['mytable'][$id]['#weight'] = $entity->get('weight');

    // Some table columns containing raw markup.
    $form['mytable'][$id]['label'] = array(
      '#plain_text' => $entity->label(),
    );
    $form['mytable'][$id]['id'] = array(
      '#plain_text' => $entity->id(),
    );

    // TableDrag: Weight column element.
    $form['mytable'][$id]['weight'] = array(
      '#type' => 'weight',
      '#title' => t('Weight for @title', array('@title' => $entity->label())),
      '#title_display' => 'invisible',
      '#default_value' => $entity->get('weight'),
      // Classify the weight element for #tabledrag.
      '#attributes' => array('class' => array('mytable-order-weight')),
    );

    // Operations (dropbutton) column.
    $form['mytable'][$id]['operations'] = array(
      '#type' => 'operations',
      '#links' => array(),
    );
    $form['mytable'][$id]['operations']['#links']['edit'] = array(
      'title' => t('Edit'),
      'url' => Url::fromRoute('mymodule.manage_edit', array('id' => $id)),
    );
    $form['mytable'][$id]['operations']['#links']['delete'] = array(
      'title' => t('Delete'),
      'url' => Url::fromRoute('mymodule.manage_delete', array('id' => $id)),
    );
  }

$form['mytable'][$id]['label'] = array(
    //'#plain_text' => $entity->ref,
    '#type' => 'number',
    '#title' => "",
    '#default_value' => $entity->ref,
    '#disabled' => TRUE,
    '#access' => FALSE,