public Collection getTimePeriodsUniqueToOtherSeries(TimeSeries series) {

        Collection result = new java.util.ArrayList();
        for (int i = 0; i < series.getItemCount(); i++) {
            RegularTimePeriod period = series.getTimePeriod(i);
            int index = getIndex(period);
            if (index < 0) {
                result.add(period);
            }
        }
        return result;