SOLR-11791: Add density Stream Evaluator

solr/core/src/java/org/apache/solr/handler/StreamHandler.java

@@ -285,6 +285,7 @@ public class StreamHandler extends RequestHandlerBase implements SolrCoreAware,
         .withFunctionName("pairedTtest", PairedTTestEvaluator.class)
         .withFunctionName("multiVariateNormalDistribution", MultiVariateNormalDistributionEvaluator.class)
         .withFunctionName("integrate", IntegrateEvaluator.class)
+        .withFunctionName("density", DensityEvaluator.class)
 
         // Boolean Stream Evaluators
 

solr/solrj/src/java/org/apache/solr/client/solrj/io/eval/DensityEvaluator.java

@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.client.solrj.io.eval;
+
+import java.io.IOException;
+import java.util.Locale;
+import java.util.List;
+
+import org.apache.commons.math3.distribution.MultivariateRealDistribution;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
+import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;
+
+public class DensityEvaluator extends RecursiveObjectEvaluator implements TwoValueWorker {
+  protected static final long serialVersionUID = 1L;
+
+  public DensityEvaluator(StreamExpression expression, StreamFactory factory) throws IOException{
+    super(expression, factory);
+  }
+
+  @Override
+  public Object doWork(Object first, Object second) throws IOException{
+
+    if (!(first instanceof MultivariateRealDistribution)) {
+      throw new IOException(String.format(Locale.ROOT, "Invalid expression %s - found type %s for the first value, expecting a MultiVariateRealDistribution for density", toExpression(constructingFactory), first.getClass().getSimpleName()));
+    }
+    if (!(second instanceof List)) {
+      throw new IOException(String.format(Locale.ROOT, "Invalid expression %s - found type %s for the second value, expecting a numeric array.", toExpression(constructingFactory), first.getClass().getSimpleName()));
+    }
+
+    MultivariateRealDistribution multivariateRealDistribution = (MultivariateRealDistribution) first;
+    List<Number> nums = (List<Number>) second;
+
+    double[] vec = new double[nums.size()];
+
+    for(int i=0; i<vec.length; i++) {
+      vec[i] = nums.get(i).doubleValue();
+    }
+
+    return multivariateRealDistribution.density(vec);
+  }
+}

solr/solrj/src/test/org/apache/solr/client/solrj/io/stream/StreamExpressionTest.java

@@ -7190,7 +7190,8 @@ public class StreamExpressionTest extends SolrCloudTestCase {
         "     f=multiVariateNormalDistribution(d, e)," +
         "     g=sample(f, 10000)," +
         "     h=cov(g)," +
-        "     i=sample(f))";
+        "     i=sample(f)," +
+        "     j=density(f, array(4.016093243274465, 138.7283428008585)))";
 
     ModifiableSolrParams paramsLoc = new ModifiableSolrParams();
     paramsLoc.set("expr", cexpr);
@@ -7224,6 +7225,9 @@ public class StreamExpressionTest extends SolrCloudTestCase {
     Number sample2 = sample.get(1);
     assertTrue(sample1.doubleValue() > -30 && sample1.doubleValue() < 30);
     assertTrue(sample2.doubleValue() > 50 && sample2.doubleValue() < 250);
+
+    Number density = (Number)tuples.get(0).get("j");
+    assertEquals(density.doubleValue(), 0.007852638121596995, .00001);
   }