SPARK-21359

[Shanshan-IC]

What changes were proposed in this pull request?

As described in https://issues.apache.org/jira/browse/SPARK-21359

add new functions for frequency discretizer transformation

How was this patch tested?

test example:
val data = Array((0, 18.0), (1, 19.0), (2, 8.0), (3, 5.0), (4, 2.2), (5, 1.0), (6, 9.1), (7, 10.1), (8, 1.1), (9, 16.0), (10, 20.0), (11, 20.0))
val df = spark.createDataFrame(data).toDF("id", "hour")
val frequency = new FrequencyDiscretizer()
.setInputCol("hour")
.setOutputCol("result")
.setNumBuckets(4)

val result = frequency.fit(df).transform(df) 
result.show() 

You will get:
+---+----+------+
| id|hour|result|
+---+----+------+
| 0|18.0| 2.0|
| 1|19.0| 3.0|
| 2| 8.0| 1.0|
| 3| 5.0| 1.0|
| 4| 2.2| 0.0|
| 5| 1.0| 0.0|
| 6| 9.1| 1.0|
| 7|10.1| 2.0|
| 8| 1.1| 0.0|
| 9|16.0| 2.0|
| 10|20.0| 3.0|
| 11|20.0| 3.0|
+---+----+------+

Please review http://spark.apache.org/contributing.html before opening a pull request.

[AmplabJenkins]

Can one of the admins verify this patch?

[srowen]

I'd ask you to close this and back up and discuss what this is about on the JIRA first. I don't understand what this is intended to do.