SearchConfigurationRankings.php

<?php

namespace Drupal\search\Plugin\migrate\process;

use Drupal\migrate\ProcessPluginBase;
use Drupal\migrate\MigrateExecutableInterface;
use Drupal\migrate\Row;

/**
 * Generate configuration rankings.
 *
 * @MigrateProcessPlugin(
 *   id = "search_configuration_rankings"
 * )
 */
class SearchConfigurationRankings extends ProcessPluginBase {
    
    /**
     * {@inheritdoc}
     *
     * Generate the configuration rankings.
     */
    public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
        $return = NULL;
        foreach ($row->getSource() as $name => $rank) {
            if (substr($name, 0, 10) == 'node_rank_' && is_numeric($rank)) {
                $return[substr($name, 10)] = $rank;
            }
        }
        return $return;
    }

}