SOLR-11401: Add zipFDistribution Stream Evaluator

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

@@ -305,6 +305,7 @@ public class StreamHandler extends RequestHandlerBase implements SolrCoreAware,
         .withFunctionName("mean", MeanEvaluator.class)
         .withFunctionName("mode", ModeEvaluator.class)
         .withFunctionName("logNormalDistribution", LogNormalDistributionEvaluator.class)
+        .withFunctionName("zipFDistribution", ZipFDistributionEvaluator.class)
 
         // Boolean Stream Evaluators
 

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

@@ -0,0 +1,48 @@
+/*
+ * 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.distribution.ZipfDistribution;
+import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
+import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;
+
+public class ZipFDistributionEvaluator extends RecursiveNumericEvaluator implements TwoValueWorker {
+
+  private static final long serialVersionUID = 1;
+
+  public ZipFDistributionEvaluator(StreamExpression expression, StreamFactory factory) throws IOException {
+    super(expression, factory);
+  }
+
+  @Override
+  public Object doWork(Object first, Object second) throws IOException{
+    if(null == first){
+      throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - null found for the first value",toExpression(constructingFactory)));
+    }
+    if(null == second){
+      throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - null found for the second value",toExpression(constructingFactory)));
+    }
+
+    Number size = (Number)first;
+    Number exp = (Number)second;
+
+    return new ZipfDistribution(size.intValue(), exp.doubleValue());
+  }
+}

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

@@ -6371,6 +6371,33 @@ public class StreamExpressionTest extends SolrCloudTestCase {
     assertEquals(cprob.doubleValue(), 0.5, 0.0);
   }
 
+  @Test
+  public void testZipFDistribution() throws Exception {
+    String cexpr = "let(a=sample(zipFDistribution(10, 1), 50000), b=freqTable(a), c=col(b, count))";
+    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> counts = (List<Number>)tuples.get(0).get("c");
+
+    assertTrue(counts.size() == 10);
+
+    int lastCount = Integer.MAX_VALUE;
+    for(Number number : counts) {
+      int current = number.intValue();
+      if(current > lastCount) {
+        throw new Exception("Zipf distribution not descending!!!");
+      } else {
+        lastCount = current;
+      }
+    }
+  }
+
   @Test
   public void testEnumeratedDistribution() throws Exception {
     String cexpr = "let(a=uniformIntegerDistribution(1, 10)," +