[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, 45 insertions, 0 deletions

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
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+++ 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()