protected override void PrintOverallResultsCore(IChannel ch, string filename, Dictionary <string, IDataView>[] metrics)
        {
            base.PrintOverallResultsCore(ch, filename, metrics);
            if (!string.IsNullOrEmpty(_groupSummaryFilename))
            {
                IDataView gs;
                if (!TryGetGroupSummaryMetrics(metrics, out gs))
                {
                    throw ch.Except("Did not find group summary metrics");
                }

                ch.Trace("Saving group-summary results");
                // If the data view contains stratification columns, filter so that only the overall metrics
                // will be present, and drop them.
                gs = MetricWriter.GetNonStratifiedMetrics(Host, gs);
                MetricWriter.SavePerInstance(Host, ch, _groupSummaryFilename, gs);
                ch.Done();
            }
        }