[SPARK-7582] [MLLIB] user guide for StringIndexer

This PR adds a Java unit test and user guide for `StringIndexer`. I put it before `OneHotEncoder` because they are closely related. jkbradley

Author: Xiangrui Meng <meng@databricks.com>

Closes #6561 from mengxr/SPARK-7582 and squashes the following commits:

4bba4f1 [Xiangrui Meng] fix example
ba1cd1b [Xiangrui Meng] fix style
7fa18d1 [Xiangrui Meng] add user guide for StringIndexer
136cb93 [Xiangrui Meng] add a Java unit test for StringIndexer

1 files changed, 77 insertions, 0 deletions

diff --git a/mllib/src/test/java/org/apache/spark/ml/feature/JavaStringIndexerSuite.java b/mllib/src/test/java/org/apache/spark/ml/feature/JavaStringIndexerSuite.java
new file mode 100644
index 0000000000..35b18c5308
--- /dev/null
+++ b/mllib/src/test/java/org/apache/spark/ml/feature/JavaStringIndexerSuite.java
@@ -0,0 +1,77 @@
+/*
+ * 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.ml.feature;
+
+import java.util.Arrays;
+
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import org.apache.spark.api.java.JavaRDD;
+import org.apache.spark.api.java.JavaSparkContext;
+import org.apache.spark.sql.DataFrame;
+import org.apache.spark.sql.Row;
+import org.apache.spark.sql.RowFactory;
+import org.apache.spark.sql.SQLContext;
+import org.apache.spark.sql.types.StructField;
+import org.apache.spark.sql.types.StructType;
+import static org.apache.spark.sql.types.DataTypes.*;
+
+public class JavaStringIndexerSuite {
+  private transient JavaSparkContext jsc;
+  private transient SQLContext sqlContext;
+
+  @Before
+  public void setUp() {
+    jsc = new JavaSparkContext("local", "JavaStringIndexerSuite");
+    sqlContext = new SQLContext(jsc);
+  }
+
+  @After
+  public void tearDown() {
+    jsc.stop();
+    sqlContext = null;
+  }
+
+  @Test
+  public void testStringIndexer() {
+    StructType schema = createStructType(new StructField[] {
+      createStructField("id", IntegerType, false),
+      createStructField("label", StringType, false)
+    });
+    JavaRDD<Row> rdd = jsc.parallelize(
+      Arrays.asList(c(0, "a"), c(1, "b"), c(2, "c"), c(3, "a"), c(4, "a"), c(5, "c")));
+    DataFrame dataset = sqlContext.createDataFrame(rdd, schema);
+
+    StringIndexer indexer = new StringIndexer()
+      .setInputCol("label")
+      .setOutputCol("labelIndex");
+    DataFrame output = indexer.fit(dataset).transform(dataset);
+
+    Assert.assertArrayEquals(
+      new Row[] { c(0, 0.0), c(1, 2.0), c(2, 1.0), c(3, 0.0), c(4, 0.0), c(5, 1.0) },
+      output.orderBy("id").select("id", "labelIndex").collect());
+  }
+
+  /** An alias for RowFactory.create. */
+  private Row c(Object... values) {
+    return RowFactory.create(values);
+  }
+}