/**
 * Implements hook_theme().
 */
function custom_theme() {
  return array(
    'multicolumn_options' => array(
    'render element' => 'form',
    ),
  );
}
 
function theme_multicolumn_options($element) {
  // Modify to dig one layer deeper.  Not sure why original code didn't need this.
  $stripped_element = array_values($element);
  $element = $stripped_element[0];
 
  // Initialize variables.
  $output = '';
  $total_columns = $element['#multicolumn_numcols'];
  $total_options = count($element['#options']);
  $options_per_column = ceil($total_options / $total_columns);
  $keys = array_keys($element['#options']);
  $type = $element[$keys[0]]['#type'];
 
  $output .= '<div class="multicolumn-options-wrapper">';
  $current_column = 1;
  $current_option = 0;
 
  while ($current_column <= $total_columns) {
    $output .=  '<div class="multicolumn-options-column" style="width: ' . 100 / $total_columns . '%; float: left">';
 
    // or you run out of options.
    while ($current_option < $options_per_column * $current_column &&
           $current_option < $total_options) {
 
      // Output as either check or radio button depending on the element type.
      $output .= drupal_render($element[$keys[$current_option]]);
      $current_option++;
    }
 
    // End column div.
    $output .= '</div>';
    $current_column++;
  }
 
  $output .= '</div>';
  $output .= '<div class="clear-both"></div>';
 
  return $output;
}
function custom_form_alter(&$form, &$form_state, $form_id) {
  if($form_id == 'THEFORMID') {
    $form['field_drupal_category']['und']['#theme'] = array('multicolumn_options');
    $form['field_drupal_category']['und']['#multicolumn_numcols'] = 4;
  }
}