Combine Facets

//Combine facet terms for Seat Material
add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'product_seat_material' == $params['facet_name'] ) {  
        $seat_material = $params['facet_value'];
        switch ( true ) {
            case ( $seat_material == '316-stainless-steel' ):
                $params['facet_value'] = 'stainless-steel';
                $params['facet_display_value'] = 'Stainless Steel';
                break;
            case ( $seat_material == '400-stainless-steel' ):
                $params['facet_value'] = 'stainless-steel';
                $params['facet_display_value'] = 'Stainless Steel';
                break;
            case ( $seat_material == 'hard-440-stainless-steel' ):
                $params['facet_value'] = 'stainless-steel';
                $params['facet_display_value'] = 'Stainless Steel';
                break; 
            case ( $seat_material == 'kynar-pvdf'):
                $params['facet_value'] = 'pvdf';
                $params['facet_display_value'] = 'PVDF';
                break;
            case ( $seat_material == 'pvdf-flex-check'):
                $params['facet_value'] = 'pvdf';
                $params['facet_display_value'] = 'PVDF';
                break;
            case ( $seat_material == 'polypropylene-flex-check'):
                $params['facet_value'] = 'polypropylene';
                $params['facet_display_value'] = 'Polypropylene';
                break;
            case ( $seat_material == 'acetal-flex-check'):
                $params['facet_value'] = 'acetal';
                $params['facet_display_value'] = 'Acetal';
                break;
      
//            default: // no value
//                $params['facet_value'] = ''; // skip indexing
        }
	} 
    return $params;
}, 10, 2 );