Github user hhbyyh commented on a diff in the pull request:
https://github.com/apache/spark/pull/21248#discussion_r189466147
--- Diff:
examples/src/main/scala/org/apache/spark/examples/ml/PowerIterationClusteringExample.scala
---
@@ -0,0 +1,114 @@
+/*
+ * 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.
+ */
+
+// scalastyle:off println
+package org.apache.spark.examples.ml
+
+import org.apache.log4j.{Level, Logger}
+
+// $example on$
+import org.apache.spark.ml.clustering.PowerIterationClustering
+// $example off$
+import org.apache.spark.sql.{DataFrame, Row, SparkSession}
+
+
+ /**
+ * An example demonstrating power iteration clustering.
+ * Run with
+ * {{{
+ * bin/run-example ml.PowerIterationClusteringExample
+ * }}}
+ */
+
+object PowerIterationClusteringExample {
+
+ def main(args: Array[String]): Unit = {
+ val spark = SparkSession
+ .builder
+ .appName(s"${this.getClass.getSimpleName}")
+ .getOrCreate()
+
+ Logger.getRootLogger.setLevel(Level.WARN)
+
+ // $example on$
+
+ // Generates data.
+ val radius1 = 1.0
+ val numPoints1 = 5
+ val radius2 = 4.0
+ val numPoints2 = 20
+
+ val dataset = generatePICData(spark, radius1, radius2, numPoints1,
numPoints2)
+
+ // Trains a PIC model.
+ val model = new PowerIterationClustering().
+ setK(2).
+ setInitMode("degree").
+ setMaxIter(20)
+
+ val prediction = model.transform(dataset).select("id", "prediction")
+
+ // Shows the result.
+ // println("Cluster Assignment: ")
+ val result = prediction.collect().map {
+ row => (row(1), row(0))
+ }.groupBy(_._1).mapValues(_.map(_._2))
+
+ result.foreach {
+ case (cluster, points) => println(s"$cluster ->
[${points.mkString(",")}]")
+ }
--- End diff --
This can be achieved by DataFrame API, groupBy.. collect_set
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