FacetWP – index a single boolean value

<?php

add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'CHANGE_ME' == $params['facet_name'] ) {
        if ( 'yes' == $params['facet_value'] ) {
            $params['facet_display_value'] = 'Yes'; // only index the "Yes" value
        }
        return false; // don't index
    }
}, 10, 2 );