[SPARK-12159][ML] Add user guide section for IndexToString transformer

Documentation regarding the `IndexToString` label transformer with code snippets in Scala/Java/Python.

Author: BenFradet <benjamin.fradet@gmail.com>

Closes #10166 from BenFradet/SPARK-12159.

1 files changed, 75 insertions, 0 deletions

diff --git a/examples/src/main/java/org/apache/spark/examples/ml/JavaIndexToStringExample.java b/examples/src/main/java/org/apache/spark/examples/ml/JavaIndexToStringExample.java
new file mode 100644
index 0000000000..3ccd699326
--- /dev/null
+++ b/examples/src/main/java/org/apache/spark/examples/ml/JavaIndexToStringExample.java
@@ -0,0 +1,75 @@
+/*
+ * 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.SparkConf;
+import org.apache.spark.api.java.JavaRDD;
+import org.apache.spark.api.java.JavaSparkContext;
+import org.apache.spark.sql.SQLContext;
+
+// $example on$
+import java.util.Arrays;
+
+import org.apache.spark.ml.feature.IndexToString;
+import org.apache.spark.ml.feature.StringIndexer;
+import org.apache.spark.ml.feature.StringIndexerModel;
+import org.apache.spark.sql.DataFrame;
+import org.apache.spark.sql.Row;
+import org.apache.spark.sql.RowFactory;
+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 JavaIndexToStringExample {
+  public static void main(String[] args) {
+    SparkConf conf = new SparkConf().setAppName("JavaIndexToStringExample");
+    JavaSparkContext jsc = new JavaSparkContext(conf);
+    SQLContext sqlContext = new SQLContext(jsc);
+
+    // $example on$
+    JavaRDD<Row> jrdd = jsc.parallelize(Arrays.asList(
+      RowFactory.create(0, "a"),
+      RowFactory.create(1, "b"),
+      RowFactory.create(2, "c"),
+      RowFactory.create(3, "a"),
+      RowFactory.create(4, "a"),
+      RowFactory.create(5, "c")
+    ));
+    StructType schema = new StructType(new StructField[]{
+      new StructField("id", DataTypes.IntegerType, false, Metadata.empty()),
+      new StructField("category", DataTypes.StringType, false, Metadata.empty())
+    });
+    DataFrame df = sqlContext.createDataFrame(jrdd, schema);
+
+    StringIndexerModel indexer = new StringIndexer()
+      .setInputCol("category")
+      .setOutputCol("categoryIndex")
+      .fit(df);
+    DataFrame indexed = indexer.transform(df);
+
+    IndexToString converter = new IndexToString()
+      .setInputCol("categoryIndex")
+      .setOutputCol("originalCategory");
+    DataFrame converted = converter.transform(indexed);
+    converted.select("id", "originalCategory").show();
+    // $example off$
+    jsc.stop();
+  }
+}