[GitHub] [druid] gianm commented on a change in pull request #10340: Fix VARIANCE aggregator comparator

[GitBox <gi...@apache.org>]

gianm commented on a change in pull request #10340:
URL: https://github.com/apache/druid/pull/10340#discussion_r482515733



##########
File path: extensions-core/stats/src/main/java/org/apache/druid/query/aggregation/variance/VarianceAggregatorFactory.java
##########
@@ -239,7 +240,9 @@ public Comparator getComparator()
   @Override
   public Object finalizeComputation(@Nullable Object object)
   {
-    return object == null ? null : ((VarianceAggregatorCollector) object).getVariance(isVariancePop);
+    return object == null || ((VarianceAggregatorCollector) object).count == 0
+           ? null

Review comment:
       Hmm, I wonder if this should be `NullHandling.defaultDoubleValue()`.
   
   Will this just happen if nothing gets read?

##########
File path: extensions-core/stats/src/main/java/org/apache/druid/query/aggregation/variance/VarianceAggregatorCollector.java
##########
@@ -60,11 +60,11 @@ public static VarianceAggregatorCollector from(ByteBuffer buffer)
   }
 
   public static final Comparator<VarianceAggregatorCollector> COMPARATOR = (o1, o2) -> {
-    int compare = Longs.compare(o1.count, o2.count);
+    int compare = Doubles.compare(o1.nvariance, o2.nvariance);

Review comment:
       Will this sort the same way as `getVariance(isVariancePop)` in `finalizeComputation`?




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