SOLR-11789: Add integrate Stream Evaluator

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

@@ -284,6 +284,7 @@ public class StreamHandler extends RequestHandlerBase implements SolrCoreAware,
         .withFunctionName("ttest", TTestEvaluator.class)
         .withFunctionName("pairedTtest", PairedTTestEvaluator.class)
         .withFunctionName("multiVariateNormalDistribution", MultiVariateNormalDistributionEvaluator.class)
+        .withFunctionName("integrate", IntegrateEvaluator.class)
 
         // Boolean Stream Evaluators
 

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

@@ -0,0 +1,70 @@
+/*
+ * 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 org.apache.commons.math3.analysis.UnivariateFunction;
+import org.apache.commons.math3.analysis.integration.RombergIntegrator;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
+import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;
+
+public class IntegrateEvaluator extends RecursiveObjectEvaluator implements ManyValueWorker {
+  protected static final long serialVersionUID = 1L;
+
+  public IntegrateEvaluator(StreamExpression expression, StreamFactory factory) throws IOException{
+    super(expression, factory);
+  }
+
+  @Override
+  public Object doWork(Object... values) throws IOException {
+
+    if(values.length != 3) {
+      throw new IOException("The integrate function requires 3 parameters");
+    }
+
+    if (!(values[0] instanceof VectorFunction)) {
+      throw new IOException(String.format(Locale.ROOT, "Invalid expression %s - found type %s for the first value, expecting a FunctionVector", toExpression(constructingFactory), values[0].getClass().getSimpleName()));
+    }
+
+    VectorFunction vectorFunction = (VectorFunction) values[0];
+    if(!(vectorFunction.getFunction() instanceof UnivariateFunction)) {
+      throw new IOException("Cannot evaluate integral from parameter.");
+    }
+
+    Number min = null;
+    Number max = null;
+
+    if(values[1] instanceof Number) {
+      min = (Number) values[1];
+    } else {
+      throw new IOException("The second parameter of the integrate function must be a number");
+    }
+
+    if(values[2] instanceof Number ) {
+      max = (Number) values[2];
+    } else {
+      throw new IOException("The third parameter of the integrate function must be a number");
+    }
+
+    UnivariateFunction func = (UnivariateFunction)vectorFunction.getFunction();
+
+    RombergIntegrator rombergIntegrator = new RombergIntegrator();
+    return rombergIntegrator.integrate(5000, func, min.doubleValue(), max.doubleValue());
+  }
+}

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

@@ -7227,6 +7227,32 @@ public class StreamExpressionTest extends SolrCloudTestCase {
   }
 
 
+  @Test
+  public void testIntegrate() throws Exception {
+    String cexpr = "let(echo=true, " +
+                       "a=sequence(50, 1, 0), " +
+                       "b=spline(a), " +
+                       "c=integrate(b, 0, 49), " +
+                       "d=integrate(b, 0, 20), " +
+                       "e=integrate(b, 20, 49))";
+    ModifiableSolrParams paramsLoc = new ModifiableSolrParams();
+    paramsLoc.set("expr", cexpr);
+    paramsLoc.set("qt", "/stream");
+    String url = cluster.getJettySolrRunners().get(0).getBaseUrl().toString()+"/"+COLLECTIONORALIAS;
+    TupleStream solrStream = new SolrStream(url, paramsLoc);
+    StreamContext context = new StreamContext();
+    solrStream.setStreamContext(context);
+    List<Tuple> tuples = getTuples(solrStream);
+    assertTrue(tuples.size() == 1);
+    Number integral = (Number)tuples.get(0).get("c");
+    assertEquals(integral.doubleValue(), 49, 0.0);
+    integral = (Number)tuples.get(0).get("d");
+    assertEquals(integral.doubleValue(), 20, 0.0);
+    integral = (Number)tuples.get(0).get("e");
+    assertEquals(integral.doubleValue(), 29, 0.0);
+  }
+
+
   @Test
   public void testLoess() throws Exception {
     String cexpr = "let(echo=true," +