Github user MLnick commented on a diff in the pull request:
https://github.com/apache/spark/pull/20446#discussion_r165362364
--- Diff:
examples/src/main/java/org/apache/spark/examples/ml/JavaSummarizerExample.java
---
@@ -0,0 +1,71 @@
+/*
+ * 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.spark.examples.ml;
+
+import org.apache.spark.sql.*;
+
+// $example on$
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.spark.ml.linalg.Vector;
+import org.apache.spark.ml.linalg.Vectors;
+import org.apache.spark.ml.linalg.VectorUDT;
+import org.apache.spark.ml.stat.Summarizer;
+import org.apache.spark.sql.types.DataTypes;
+import org.apache.spark.sql.types.Metadata;
+import org.apache.spark.sql.types.StructField;
+import org.apache.spark.sql.types.StructType;
+// $example off$
+
+public class JavaSummarizerExample {
+ public static void main(String[] args) {
+ SparkSession spark = SparkSession
+ .builder()
+ .appName("JavaSummarizerExample")
+ .getOrCreate();
+
+ // $example on$
+ List<Row> data = Arrays.asList(
+ RowFactory.create(Vectors.dense(2.0, 3.0, 5.0), 1.0),
+ RowFactory.create(Vectors.dense(4.0, 6.0, 7.0), 2.0)
+ );
+
+ StructType schema = new StructType(new StructField[]{
+ new StructField("features", new VectorUDT(), false,
Metadata.empty()),
+ new StructField("weight", DataTypes.DoubleType, false,
Metadata.empty())
+ });
+
+ Dataset<Row> df = spark.createDataFrame(data, schema);
+
+ Row result1 = df.select(Summarizer.metrics("mean", "variance")
+ .summary(new Column("features"), new Column("weight")))
+ .first().getStruct(0);
+ System.out.println("with weight: mean = " +
result1.<Vector>getAs(0).toString() +
--- End diff --
Why not just `df.select(...).show()`?
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