question: protected Metric reduce ( List < Metric > metrics ) { SystemAssert . requireArgument ( metrics != null , "Cannot transform empty metric/metrics" ) ; MetricDistiller distiller = new MetricDistiller ( ) ; distiller . distill ( metrics ) ; Map < Long , List < String > > collated = collate ( metrics ) ; Map < Long , String > minDatapoints = reduce ( collated , metrics ) ; String newMetricName = distiller . getMetric ( ) == null ? defaultMetricName : distiller . getMetric ( ) ; Metric newMetric = new Metric ( defaultScope , newMetricName ) ; newMetric . setDisplayName ( distiller . getDisplayName ( ) ) ; newMetric . setUnits ( distiller . getUnits ( ) ) ; newMetric . setTags ( distiller . getTags ( ) ) ; newMetric . setDatapoints ( minDatapoints ) ; return newMetric ; }
target:  Reduce transform for the list of metrics.