facetwp add view all radio button

custom-hooks.php

<?php
/** adds a "View All" index value to every post
 ** change 'my_radio' to the name of the radio facet to apply to
 ** 'View All' can be changed to whatever label is preferred
 ** reindex after add this code
 **/

add_filter( 'facetwp_indexer_row_data', function( $rows, $params ) {
  if ( 'my_radio' == $params['facet']['name'] ) {
    $new_row = $params['defaults'];
    $new_row['facet_value'] = 'all';
    $new_row['facet_display_value'] = 'View All';
    $rows[] = $new_row;
  }
  return $rows;
}, 10, 2 );