[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, 60 insertions, 0 deletions

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