[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.

3 files changed, 180 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();
+  }
+}
diff --git a/examples/src/main/python/ml/index_to_string_example.py b/examples/src/main/python/ml/index_to_string_example.py
new file mode 100644
index 0000000000..fb0ba2950b
--- /dev/null
+++ b/examples/src/main/python/ml/index_to_string_example.py
@@ -0,0 +1,45 @@
+#
+# 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.
+#
+
+from __future__ import print_function
+
+from pyspark import SparkContext
+# $example on$
+from pyspark.ml.feature import IndexToString, StringIndexer
+# $example off$
+from pyspark.sql import SQLContext
+
+if __name__ == "__main__":
+    sc = SparkContext(appName="IndexToStringExample")
+    sqlContext = SQLContext(sc)
+
+    # $example on$
+    df = sqlContext.createDataFrame(
+        [(0, "a"), (1, "b"), (2, "c"), (3, "a"), (4, "a"), (5, "c")],
+        ["id", "category"])
+
+    stringIndexer = StringIndexer(inputCol="category", outputCol="categoryIndex")
+    model = stringIndexer.fit(df)
+    indexed = model.transform(df)
+
+    converter = IndexToString(inputCol="categoryIndex", outputCol="originalCategory")
+    converted = converter.transform(indexed)
+
+    converted.select("id", "originalCategory").show()
+    # $example off$
+
+    sc.stop()
diff --git a/examples/src/main/scala/org/apache/spark/examples/ml/IndexToStringExample.scala b/examples/src/main/scala/org/apache/spark/examples/ml/IndexToStringExample.scala
new file mode 100644
index 0000000000..52537e5bb5
--- /dev/null
+++ b/examples/src/main/scala/org/apache/spark/examples/ml/IndexToStringExample.scala
@@ -0,0 +1,60 @@
+/*
+ * 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.spark.sql.SQLContext
+import org.apache.spark.{SparkConf, SparkContext}
+// $example on$
+import org.apache.spark.ml.feature.{StringIndexer, IndexToString}
+// $example off$
+
+object IndexToStringExample {
+  def main(args: Array[String]) {
+    val conf = new SparkConf().setAppName("IndexToStringExample")
+    val sc = new SparkContext(conf)
+
+    val sqlContext = SQLContext.getOrCreate(sc)
+
+    // $example on$
+    val df = sqlContext.createDataFrame(Seq(
+      (0, "a"),
+      (1, "b"),
+      (2, "c"),
+      (3, "a"),
+      (4, "a"),
+      (5, "c")
+    )).toDF("id", "category")
+
+    val indexer = new StringIndexer()
+      .setInputCol("category")
+      .setOutputCol("categoryIndex")
+      .fit(df)
+    val indexed = indexer.transform(df)
+
+    val converter = new IndexToString()
+      .setInputCol("categoryIndex")
+      .setOutputCol("originalCategory")
+
+    val converted = converter.transform(indexed)
+    converted.select("id", "originalCategory").show()
+    // $example off$
+    sc.stop()
+  }
+}
+// scalastyle:on println