Allow meta filtering of the PMPro membership directory

my_add_meta_queries_to_pmpro_directory_search.php

/**
 * Allow meta filtering of the membership directory
 * if pk and ps params are passed into the URL.
 * PMPro and the PMPro Member Directory Add Ons should be active.
 * Then add this code to a custom plugin.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_add_meta_queries_to_pmpro_directory_search( $sql_parts ) {
	global $wpdb;
	
	// get the meta key and search terms
	if(isset($_REQUEST['ps'])) {
		$s = sanitize_text_field( $_REQUEST['ps'] );
	} else {
		$s = "";
	}
		
	if(isset($_REQUEST['pk'])) {
		$key = sanitize_text_field( $_REQUEST['pk'] );
	} else {
		$key = "";
	}
	
	// add meta filtering if passed in
	if ( !empty( $s ) && !empty( $key ) ) {
		$sql_parts['JOIN'] .= " LEFT JOIN $wpdb->usermeta umk ON umk.meta_key = '" . esc_sql( $key ) . "' AND umk.user_id = u.ID ";
		$sql_parts['WHERE'] .= " AND umk.meta_value LIKE '%" . esc_sql( $s ) . "%' ";
	}
	
	return $sql_parts;
}
add_filter( 'pmpro_member_directory_sql_parts', 'my_add_meta_queries_to_pmpro_directory_search' );