Drupal move all data from one field to another on the same node programatically.

gistfile1.txt

/**
 * Move all data in one field to another.
 * In the example below we replace a multi cardinality field (field_old_field)
 * with a single cardinality field (field_new_field).
 * The data in the first element of the old field becomes the only data in the new field.
 * 
 * @requires entity module
 */
function mymodule_update_7001(&$sandbox) {
  if (!isset($sandbox['progress'])) {
    $query = new EntityFieldQuery();
    $count = $query->entityCondition('entity_type', 'node', '=')
      ->entityCondition('bundle', 'page')
      ->count()
      ->execute();

    $sandbox['progress'] = 0;
    $sandbox['max'] = $count;

    watchdog('mymodule', 'Going to process :count page', array(':count' => $count));
  }

  $query = new EntityFieldQuery();
  $results = $query->entityCondition('entity_type', 'node', '=')
    ->entityCondition('bundle', 'page')
    ->range($sandbox['progress'], 10)
    ->execute();

  $node_ids = empty($results['node']) ? array() : array_keys($results['node']);

  foreach ($node_ids as $node_id) {
    try {
      $node_wrapper = entity_metadata_wrapper('node', $node_id);
      $node_wrapper->field_new_field->set($node_wrapper->field_old_field[0]->value());
      $node_wrapper->save();
    }
    catch (Exception $e) {
      watchdog('mymodule', 'Problem with node @node_id', array('@node_id' => $node_id), WATCHDOG_ERROR);
    }
    $sandbox['progress']++;
  }

  watchdog('mymodule', 'Processed :progress / :count page', array(
    ':progress' => $sandbox['progress'],
    ':count' => $sandbox['max'],
  ));

  $sandbox['#finished'] = empty($sandbox['max']) || empty($node_ids) ? 1 : ($sandbox['progress'] / $sandbox['max']);
}

Thanks for sharing this. How does your sandbox work?

Oh ahaha here is a great explanation http://bleen.net/blog/running-batch-processes-update-hook-bed