Add aggregator for calculating the population standard deviation

1 files changed, 90 insertions, 0 deletions

diff --git a/searchlib/src/main/java/com/yahoo/searchlib/aggregation/StandardDeviationAggregationResult.java b/searchlib/src/main/java/com/yahoo/searchlib/aggregation/StandardDeviationAggregationResult.java
new file mode 100644
index 00000000000..4edeec7ba77
--- /dev/null
+++ b/searchlib/src/main/java/com/yahoo/searchlib/aggregation/StandardDeviationAggregationResult.java
@@ -0,0 +1,90 @@
+// Copyright 2017 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.searchlib.aggregation;
+
+import com.yahoo.searchlib.expression.FloatResultNode;
+import com.yahoo.searchlib.expression.ResultNode;
+import com.yahoo.vespa.objects.Deserializer;
+import com.yahoo.vespa.objects.ObjectVisitor;
+import com.yahoo.vespa.objects.Serializer;
+
+/**
+ * @author bjorncs
+ */
+public class StandardDeviationAggregationResult extends AggregationResult  {
+    public static final int classId = registerClass(0x4000 + 89, StandardDeviationAggregationResult.class);
+
+    private long count;
+    private double sum;
+    private double sumOfSquared;
+
+    /**
+     * Constructor used for deserialization. Will be instantiated with a default sketch.
+     */
+    @SuppressWarnings("unused")
+    public StandardDeviationAggregationResult() {
+        this(0, 0.0, 0.0);
+    }
+
+    public StandardDeviationAggregationResult(long count, double sum, double sumOfSquared) {
+        this.count = count;
+        this.sum = sum;
+        this.sumOfSquared = sumOfSquared;
+    }
+
+    public double getStandardDeviation() {
+        if (count == 0) {
+            return 0;
+        } else {
+            double variance = (sumOfSquared - sum * sum / count) / count;
+            return Math.sqrt(variance);
+        }
+    }
+
+    @Override
+    public ResultNode getRank() {
+        return new FloatResultNode(getStandardDeviation());
+    }
+
+    @Override
+    protected void onMerge(AggregationResult obj) {
+        StandardDeviationAggregationResult other = (StandardDeviationAggregationResult) obj;
+        count += other.count;
+        sum += other.sum;
+        sumOfSquared += other.sumOfSquared;
+    }
+
+    @Override
+    protected boolean equalsAggregation(AggregationResult obj) {
+        StandardDeviationAggregationResult other = (StandardDeviationAggregationResult) obj;
+        return count == this.count && sum == other.sum && sumOfSquared == other.sumOfSquared;
+    }
+
+    @Override
+    protected void onSerialize(Serializer buf) {
+        super.onSerialize(buf);
+        buf.putLong(null, count);
+        buf.putDouble(null, sum);
+        buf.putDouble(null, sumOfSquared);
+    }
+
+    @Override
+    protected void onDeserialize(Deserializer buf) {
+        super.onDeserialize(buf);
+        count = buf.getLong(null);
+        sum = buf.getDouble(null);
+        sumOfSquared = buf.getDouble(null);
+    }
+
+    @Override
+    protected int onGetClassId() {
+        return classId;
+    }
+
+    @Override
+    public void visitMembers(ObjectVisitor visitor) {
+        super.visitMembers(visitor);
+        visitor.visit("count", count);
+        visitor.visit("sum", sum);
+        visitor.visit("sumOfSquared", sumOfSquared);
+    }
+}