bp_notifications_get_grouped_notifications_for_user( int $user_id )

function bp_notifications_get_grouped_notifications_for_user( $user_id = 0 ) {
	if ( empty( $user_id ) ) {
		$user_id = ( bp_displayed_user_id() ) ? bp_displayed_user_id() : bp_loggedin_user_id();
	}

	$notifications = wp_cache_get( $user_id, 'bp_notifications_grouped_notifications' );
	if ( false === $notifications ) {
		$notifications = BP_Notifications_Notification::get_grouped_notifications_for_user( $user_id );
		wp_cache_set( $user_id, $notifications, 'bp_notifications_grouped_notifications' );
	}

	return $notifications;
}