[SPARK-7577] [ML] [DOC] add bucketizer doc

CC jkbradley

Author: Xusen Yin <yinxusen@gmail.com>

Closes #6451 from yinxusen/SPARK-7577 and squashes the following commits:

e2dc32e [Xusen Yin] rename colums
e350e49 [Xusen Yin] add all demos
006ddf1 [Xusen Yin] add java test
3238481 [Xusen Yin] add bucketizer

docs/ml-features.md

@@ -789,6 +789,92 @@ scaledData = scalerModel.transform(dataFrame)
 </div>
 </div>
 
+## Bucketizer
+
+`Bucketizer` transforms a column of continuous features to a column of feature buckets, where the buckets are specified by users. It takes a parameter:
+
+* `splits`: Parameter for mapping continuous features into buckets. With n+1 splits, there are n buckets. A bucket defined by splits x,y holds values in the range [x,y) except the last bucket, which also includes y. Splits should be strictly increasing. Values at -inf, inf must be explicitly provided to cover all Double values; Otherwise, values outside the splits specified will be treated as errors. Two examples of `splits` are `Array(Double.NegativeInfinity, 0.0, 1.0, Double.PositiveInfinity)` and `Array(0.0, 1.0, 2.0)`.
+
+Note that if you have no idea of the upper bound and lower bound of the targeted column, you would better add the `Double.NegativeInfinity` and `Double.PositiveInfinity` as the bounds of your splits to prevent a potenial out of Bucketizer bounds exception.
+
+Note also that the splits that you provided have to be in strictly increasing order, i.e. `s0 < s1 < s2 < ... < sn`.
+
+More details can be found in the API docs for [Bucketizer](api/scala/index.html#org.apache.spark.ml.feature.Bucketizer).
+
+The following example demonstrates how to bucketize a column of `Double`s into another index-wised column.
+
+<div class="codetabs">
+<div data-lang="scala">
+{% highlight scala %}
+import org.apache.spark.ml.feature.Bucketizer
+import org.apache.spark.sql.DataFrame
+
+val splits = Array(Double.NegativeInfinity, -0.5, 0.0, 0.5, Double.PositiveInfinity)
+
+val data = Array(-0.5, -0.3, 0.0, 0.2)
+val dataFrame = sqlContext.createDataFrame(data.map(Tuple1.apply)).toDF("features")
+
+val bucketizer = new Bucketizer()
+  .setInputCol("features")
+  .setOutputCol("bucketedFeatures")
+  .setSplits(splits)
+
+// Transform original data into its bucket index.
+val bucketedData = bucketizer.transform(dataFrame)
+{% endhighlight %}
+</div>
+
+<div data-lang="java">
+{% highlight java %}
+import com.google.common.collect.Lists;
+
+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;
+
+double[] splits = {Double.NEGATIVE_INFINITY, -0.5, 0.0, 0.5, Double.POSITIVE_INFINITY};
+
+JavaRDD<Row> data = jsc.parallelize(Lists.newArrayList(
+  RowFactory.create(-0.5),
+  RowFactory.create(-0.3),
+  RowFactory.create(0.0),
+  RowFactory.create(0.2)
+));
+StructType schema = new StructType(new StructField[] {
+  new StructField("features", DataTypes.DoubleType, false, Metadata.empty())
+});
+DataFrame dataFrame = jsql.createDataFrame(data, schema);
+
+Bucketizer bucketizer = new Bucketizer()
+  .setInputCol("features")
+  .setOutputCol("bucketedFeatures")
+  .setSplits(splits);
+
+// Transform original data into its bucket index.
+DataFrame bucketedData = bucketizer.transform(dataFrame);
+{% endhighlight %}
+</div>
+
+<div data-lang="python">
+{% highlight python %}
+from pyspark.ml.feature import Bucketizer
+
+splits = [-float("inf"), -0.5, 0.0, 0.5, float("inf")]
+
+data = [(-0.5,), (-0.3,), (0.0,), (0.2,)]
+dataFrame = sqlContext.createDataFrame(data, ["features"])
+
+bucketizer = Bucketizer(splits=splits, inputCol="features", outputCol="bucketedFeatures")
+
+# Transform original data into its bucket index.
+bucketedData = bucketizer.transform(dataFrame)
+{% endhighlight %}
+</div>
+</div>
 
 # Feature Selectors
 

mllib/src/test/java/org/apache/spark/ml/feature/JavaBucketizerSuite.java

@@ -0,0 +1,80 @@
+/*
+ * 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 com.google.common.collect.Lists;
+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.DataTypes;
+import org.apache.spark.sql.types.Metadata;
+import org.apache.spark.sql.types.StructField;
+import org.apache.spark.sql.types.StructType;
+
+public class JavaBucketizerSuite {
+  private transient JavaSparkContext jsc;
+  private transient SQLContext jsql;
+
+  @Before
+  public void setUp() {
+    jsc = new JavaSparkContext("local", "JavaBucketizerSuite");
+    jsql = new SQLContext(jsc);
+  }
+
+  @After
+  public void tearDown() {
+    jsc.stop();
+    jsc = null;
+  }
+
+  @Test
+  public void bucketizerTest() {
+    double[] splits = {-0.5, 0.0, 0.5};
+
+    JavaRDD<Row> data = jsc.parallelize(Lists.newArrayList(
+      RowFactory.create(-0.5),
+      RowFactory.create(-0.3),
+      RowFactory.create(0.0),
+      RowFactory.create(0.2)
+    ));
+    StructType schema = new StructType(new StructField[] {
+      new StructField("feature", DataTypes.DoubleType, false, Metadata.empty())
+    });
+    DataFrame dataset = jsql.createDataFrame(data, schema);
+
+    Bucketizer bucketizer = new Bucketizer()
+      .setInputCol("feature")
+      .setOutputCol("result")
+      .setSplits(splits);
+
+    Row[] result = bucketizer.transform(dataset).select("result").collect();
+
+    for (Row r : result) {
+      double index = r.getDouble(0);
+      Assert.assertTrue((index >= 0) && (index <= 1));
+    }
+  }
+}