SOLR-11572: Add recip Stream Evaluator to support reciprocal transformations

solr/solrj/src/java/org/apache/solr/client/solrj/io/Lang.java

@@ -272,6 +272,7 @@ public class Lang {
         .withFunctionName("getRadius", GetRadiusEvaluator.class)
         .withFunctionName("getSupportPoints", GetSupportPointsEvaluator.class)
         .withFunctionName("pairSort", PairSortEvaluator.class)
+        .withFunctionName("recip", RecipEvaluator.class)
         // Boolean Stream Evaluators
 
         .withFunctionName("and", AndEvaluator.class)

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

@@ -0,0 +1,52 @@
+/*
+ * 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.List;
+import java.util.Locale;
+import java.util.stream.Collectors;
+
+import org.apache.commons.math3.analysis.function.Inverse;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
+import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;
+
+public class RecipEvaluator extends RecursiveNumericEvaluator implements OneValueWorker {
+  protected static final long serialVersionUID = 1L;
+
+  public RecipEvaluator(StreamExpression expression, StreamFactory factory) throws IOException{
+    super(expression, factory);
+
+    if(1 != containedEvaluators.size()){
+      throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - expecting exactly 1 value but found %d",expression,containedEvaluators.size()));
+    }
+  }
+
+  @Override
+  public Object doWork(Object value){
+    if(null == value) {
+      return null;
+    }
+    else if(value instanceof List) {
+      return ((List<?>)value).stream().map(innerValue -> doWork(innerValue)).collect(Collectors.toList());
+    }
+    else{
+      Inverse inverse = new Inverse();
+      return inverse.value(((Number)value).doubleValue());
+    }
+  }
+}

solr/solrj/src/test/org/apache/solr/client/solrj/io/TestLang.java

@@ -73,7 +73,7 @@ public class TestLang extends LuceneTestCase {
       "outliers", "stream", "getCache", "putCache", "listCache", "removeCache", "zscores", "latlonVectors",
       "convexHull", "getVertices", "getBaryCenter", "getArea", "getBoundarySize","oscillate",
       "getAmplitude", "getPhase", "getAngularFrequency", "enclosingDisk", "getCenter", "getRadius",
-      "getSupportPoints", "pairSort", "log10", "plist"};
+      "getSupportPoints", "pairSort", "log10", "plist", "recip"};
 
   @Test
   public void testLang() {

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

@@ -1800,6 +1800,31 @@ public class MathExpressionTest extends SolrCloudTestCase {
     assertEquals(log.doubleValue(), 1.4842998393467859, 0.0);
   }
 
+
+  @Test
+  public void testRecip() throws Exception {
+    String cexpr = "let(echo=true, a=array(10, 20, 30), b=recip(a), c=recip(30.5))";
+    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);
+    assertEquals(tuples.size(), 1);
+    Tuple tuple = tuples.get(0);
+    List<Number> logs = (List<Number>)tuple.get("b");
+    assertEquals(logs.size(), 3);
+    assertEquals(logs.get(0).doubleValue(), .1, 0.0);
+    assertEquals(logs.get(1).doubleValue(), .05, 0.0);
+    assertEquals(logs.get(2).doubleValue(), 0.03333333333333333, 0.0);
+
+    Number log = (Number)tuple.get("c");
+    assertEquals(log.doubleValue(), 0.03278688524590164, 0.0);
+  }
+
+
   @Test
   public void testPow() throws Exception {
     String cexpr = "let(echo=true, a=array(10, 20, 30), b=pow(a, 2), c=pow(2, a), d=pow(10, 3), e=pow(a, array(1, 2, 3)))";