add sum of squares, variance, and std deviation for statistical facet

modules/elasticsearch/src/main/java/org/elasticsearch/search/facets/statistical/InternalStatisticalFacet.java

@@ -40,16 +40,19 @@ public class InternalStatisticalFacet implements StatisticalFacet, InternalFacet
 
     private double total;
 
+    private double sumOfSquares;
+
     private long count;
 
     private InternalStatisticalFacet() {
     }
 
-    public InternalStatisticalFacet(String name, double min, double max, double total, long count) {
+    public InternalStatisticalFacet(String name, double min, double max, double total, double sumOfSquares, long count) {
         this.name = name;
         this.min = min;
         this.max = max;
         this.total = total;
+        this.sumOfSquares = sumOfSquares;
         this.count = count;
     }
 
@@ -85,6 +88,14 @@ public class InternalStatisticalFacet implements StatisticalFacet, InternalFacet
         return total();
     }
 
+    @Override public double sumOfSquares() {
+        return this.sumOfSquares;
+    }
+
+    @Override public double getSumOfSquares() {
+        return sumOfSquares();
+    }
+
     @Override public double mean() {
         return total / count;
     }
@@ -109,10 +120,27 @@ public class InternalStatisticalFacet implements StatisticalFacet, InternalFacet
         return max();
     }
 
+    public double variance() {
+        return (sumOfSquares - ((total * total) / count)) / count;
+    }
+
+    public double getVariance() {
+        return variance();
+    }
+
+    public double stdDeviation() {
+        return Math.sqrt(variance());
+    }
+
+    public double getStdDeviation() {
+        return stdDeviation();
+    }
+
     @Override public Facet aggregate(Iterable<Facet> facets) {
-        double min = Double.MAX_VALUE;
-        double max = Double.MIN_VALUE;
+        double min = Double.NaN;
+        double max = Double.NaN;
         double total = 0;
+        double sumOfSquares = 0;
         long count = 0;
 
         for (Facet facet : facets) {
@@ -120,26 +148,31 @@ public class InternalStatisticalFacet implements StatisticalFacet, InternalFacet
                 continue;
             }
             InternalStatisticalFacet statsFacet = (InternalStatisticalFacet) facet;
-            if (statsFacet.min() < min) {
+            if (statsFacet.min() < min || Double.isNaN(min)) {
                 min = statsFacet.min();
             }
-            if (statsFacet.max() > max) {
+            if (statsFacet.max() > max || Double.isNaN(max)) {
                 max = statsFacet.max();
             }
             total += statsFacet.total();
+            sumOfSquares += statsFacet.sumOfSquares();
             count += statsFacet.count();
         }
 
-        return new InternalStatisticalFacet(name, min, max, total, count);
+        return new InternalStatisticalFacet(name, min, max, total, sumOfSquares, count);
     }
 
     @Override public void toXContent(XContentBuilder builder, Params params) throws IOException {
         builder.startObject(name);
         builder.field("_type", "statistical");
-        builder.field("count", count);
-        builder.field("total", total);
-        builder.field("min", min);
-        builder.field("max", max);
+        builder.field("count", count());
+        builder.field("total", total());
+        builder.field("min", min());
+        builder.field("max", max());
+        builder.field("mean", mean());
+        builder.field("sum_of_squares", sumOfSquares());
+        builder.field("variance", variance());
+        builder.field("std_deviation", stdDeviation());
         builder.endObject();
     }
 

modules/elasticsearch/src/main/java/org/elasticsearch/search/facets/statistical/StatisticalFacet.java

@@ -48,6 +48,16 @@ public interface StatisticalFacet extends Facet {
      */
     double getTotal();
 
+    /**
+     * The sum of squares of the values.
+     */
+    double sumOfSquares();
+
+    /**
+     * The sum of squares of the values.
+     */
+    double getSumOfSquares();
+
     /**
      * The mean (average) of the values.
      */
@@ -77,4 +87,24 @@ public interface StatisticalFacet extends Facet {
      * The maximum value.
      */
     double getMax();
+
+    /**
+     * Variance of the values.
+     */
+    double variance();
+
+    /**
+     * Variance of the values.
+     */
+    double getVariance();
+
+    /**
+     * Standard deviation of the values.
+     */
+    double stdDeviation();
+
+    /**
+     * Standard deviation of the values.
+     */
+    double getStdDeviation();
 }

modules/elasticsearch/src/main/java/org/elasticsearch/search/facets/statistical/StatisticalFacetCollector.java

@@ -79,44 +79,51 @@ public class StatisticalFacetCollector extends FacetCollector {
     }
 
     @Override public Facet facet() {
-        return new InternalStatisticalFacet(name, statsProc.min(), statsProc.max(), statsProc.total(), statsProc.count());
+        return new InternalStatisticalFacet(name, statsProc.min(), statsProc.max(), statsProc.total(), statsProc.sumOfSquares(), statsProc.count());
     }
 
     public static class StatsProc implements NumericFieldData.DoubleValueInDocProc {
 
-        private double min = Double.MAX_VALUE;
+        private double min = Double.NaN;
 
-        private double max = Double.MIN_VALUE;
+        private double max = Double.NaN;
 
         private double total = 0;
 
+        private double sumOfSquares = 0.0;
+
         private long count;
 
         @Override public void onValue(int docId, double value) {
-            count++;
-            total += value;
-            if (value < min) {
+            if (value < min || Double.isNaN(min)) {
                 min = value;
             }
-            if (value > max) {
+            if (value > max || Double.isNaN(max)) {
                 max = value;
             }
+            sumOfSquares += value * value;
+            total += value;
+            count++;
         }
 
-        public double min() {
+        public final double min() {
             return min;
         }
 
-        public double max() {
+        public final double max() {
             return max;
         }
 
-        public double total() {
+        public final double total() {
             return total;
         }
 
-        public long count() {
+        public final long count() {
             return count;
         }
+
+        public final double sumOfSquares() {
+            return sumOfSquares;
+        }
     }
 }

modules/test/integration/src/test/java/org/elasticsearch/test/integration/search/facets/SimpleFacetsTests.java

@@ -124,6 +124,7 @@ public class SimpleFacetsTests extends AbstractNodesTests {
         assertThat(facet.min(), equalTo(1d));
         assertThat(facet.max(), equalTo(2d));
         assertThat(facet.mean(), equalTo(1.5d));
+        assertThat(facet.sumOfSquares(), equalTo(5d));
 
         facet = searchResponse.facets().facet(StatisticalFacet.class, "stats2");
         assertThat(facet.name(), equalTo(facet.name()));