function content_statistics_node_view(EntityInterface $node, EntityDisplay $display, $view_mode) {
    $node_count = some function called;
    foreach ($node_count as $key => $value) {
      $node_statistics = array(
        '#theme' => 'content_statistics_list',
        '#letter' => $value->letter,
        '#word' => $value->word,
        '#sentence' => $value->sentence,
      );
    }
  }
  $node->content['content_statistics_list'] = array(
    '#markup' => drupal_render($node_statistics)
  );
}

/**
 * Implements hook_theme().
 */
function content_statistics_theme($existing, $type, $theme, $path) {
   return array(
    'content_statistics_list' => array(
      'variables' => array('letter' => NULL, 'word' => NULL, 'sentence' => NULL),
      'template' =>  drupal_get_path('module', 'content_statistics') . '/templates/' . 'content-statistics-list',
    ),
  );
}