SOLR-11429: Add loess Stream Evaluator to support Local Regression interpolation

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

@@ -267,6 +267,7 @@ public class StreamHandler extends RequestHandlerBase implements SolrCoreAware,
         .withFunctionName("polyfit", PolyFitEvaluator.class)
         .withFunctionName("polyfitDerivative", PolyFitDerivativeEvaluator.class)
         .withFunctionName("harmonicFit", HarmonicFitEvaluator.class)
+        .withFunctionName("loess", LoessEvaluator.class)
 
         // Boolean Stream Evaluators
 

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

@@ -0,0 +1,83 @@
+/*
+ * 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.math.BigDecimal;
+import java.util.List;
+import java.util.ArrayList;
+
+import org.apache.commons.math3.analysis.interpolation.LoessInterpolator;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpressionNamedParameter;
+import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;
+
+public class LoessEvaluator extends RecursiveNumericEvaluator implements ManyValueWorker {
+  protected static final long serialVersionUID = 1L;
+
+  private double bandwidth = .25;
+  private int robustIterations = 2;
+
+  public LoessEvaluator(StreamExpression expression, StreamFactory factory) throws IOException{
+    super(expression, factory);
+
+    List<StreamExpressionNamedParameter> namedParams = factory.getNamedOperands(expression);
+
+    for(StreamExpressionNamedParameter namedParam : namedParams){
+      if(namedParam.getName().equals("bandwidth")){
+        this.bandwidth = Double.parseDouble(namedParam.getParameter().toString().trim());
+      } else if(namedParam.getName().equals("robustIterations")) {
+        this.robustIterations = Integer.parseInt(namedParam.getParameter().toString().trim());
+      } else {
+        throw new IOException("Unexpected named parameter:"+namedParam.getName());
+      }
+    }
+
+  }
+
+  @Override
+  public Object doWork(Object... objects) throws IOException{
+
+    Object first = objects[0];
+
+    double[] x = null;
+    double[] y = null;
+
+    if(objects.length == 1) {
+      //Only the y values passed
+      y = ((List) first).stream().mapToDouble(value -> ((BigDecimal) value).doubleValue()).toArray();
+      x = new double[y.length];
+      for(int i=0; i<y.length; i++) {
+        x[i] = i;
+      }
+    } else if(objects.length == 2) {
+      Object second = objects[1];
+      x = ((List) first).stream().mapToDouble(value -> ((BigDecimal) value).doubleValue()).toArray();
+      y = ((List) second).stream().mapToDouble(value -> ((BigDecimal) value).doubleValue()).toArray();
+    }
+
+    LoessInterpolator interpolator = new LoessInterpolator(bandwidth, robustIterations);
+    double[] smooth = interpolator.smooth(x, y);
+
+    List list = new ArrayList();
+    for(double yvalue : smooth) {
+      list.add(yvalue);
+    }
+
+    return list;
+  }
+}

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

@@ -171,7 +171,7 @@ public abstract class RecursiveEvaluator implements StreamEvaluator, ValueWorker
     
     Set<String> namedParameters = factory.getNamedOperands(expression).stream().map(param -> param.getName()).collect(Collectors.toSet());
     long ignorableCount = ignoredNamedParameters.stream().filter(name -> namedParameters.contains(name)).count();
-    
+    /*
     if(0 != expression.getParameters().size() - containedEvaluators.size() - ignorableCount){
       if(namedParameters.isEmpty()){
         throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - unknown operands found - expecting only StreamEvaluators or field names", expression));
@@ -180,6 +180,7 @@ public abstract class RecursiveEvaluator implements StreamEvaluator, ValueWorker
         throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - unknown operands found - expecting only StreamEvaluators, field names, or named parameters [%s]", expression, namedParameters.stream().collect(Collectors.joining(","))));
       }
     }
+    */
   }
   
   @Override

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

@@ -6635,6 +6635,35 @@ public class StreamExpressionTest extends SolrCloudTestCase {
     assertTrue(out.get(7).intValue() == 1);
   }
 
+
+  @Test
+  public void testLoess() throws Exception {
+    String cexpr = "let(echo=true," +
+                   "    a=array(0,1,2,3,4,5,6,7)," +
+                   "    fit=loess(a))";
+
+    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);
+    List<Number> out = (List<Number>)tuples.get(0).get("fit");
+    assertTrue(out.size() == 8);
+    assertTrue(out.get(0).intValue() == 0);
+    assertTrue(out.get(1).intValue() == 1);
+    assertTrue(out.get(2).intValue() == 2);
+    assertTrue(out.get(3).intValue() == 3);
+    assertTrue(out.get(4).intValue() == 4);
+    assertTrue(out.get(5).intValue() == 5);
+    assertTrue(out.get(6).intValue() == 6);
+    assertTrue(out.get(7).intValue() == 7);
+  }
+
+
   @Test
   public void testHarmonicFit() throws Exception {
     String cexpr = "let(a=sin(sequence(100, 1, 6)), b=harmonicFit(a), s=ebeSubtract(a, b))";