Don't recalculate UDF [duplicate] - scala

Question

i have a dataframe with a parquet file and I have to add a new column with some random data, but I need that random data different each other. This is my actual code and the current version of spark is 1.5.1-cdh-5.5.2:
val mydf = sqlContext.read.parquet("some.parquet")
// mydf.count()
// 63385686
mydf.cache
val r = scala.util.Random
import org.apache.spark.sql.functions.udf
def myNextPositiveNumber :String = { (r.nextInt(Integer.MAX_VALUE) + 1 ).toString.concat("D")}
val myFunction = udf(myNextPositiveNumber _)
val myNewDF = mydf.withColumn("myNewColumn",lit(myNextPositiveNumber))
with this code, I have this data:
scala> myNewDF.select("myNewColumn").show(10,false)
+-----------+
|myNewColumn|
+-----------+
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
|889488717D |
+-----------+
It looks like that the udf myNextPositiveNumber is invoked only once, isn't?
update
confirmed, there is only one distinct value:
scala> myNewDF.select("myNewColumn").distinct.show(50,false)
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
17/02/21 13:23:11 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
...
+-----------+
|myNewColumn|
+-----------+
|889488717D |
+-----------+
what do I am doing wrong?
Update 2: finally, with the help of #user6910411 I have this code:
val mydf = sqlContext.read.parquet("some.parquet")
// mydf.count()
// 63385686
mydf.cache
val r = scala.util.Random
import org.apache.spark.sql.functions.udf
val accum = sc.accumulator(1)
def myNextPositiveNumber():String = {
accum+=1
accum.value.toString.concat("D")
}
val myFunction = udf(myNextPositiveNumber _)
val myNewDF = mydf.withColumn("myNewColumn",lit(myNextPositiveNumber))
myNewDF.select("myNewColumn").count
// 63385686
update 3
Actual code generates data like this:
scala> mydf.select("myNewColumn").show(5,false)
17/02/22 11:01:57 WARN ParquetRecordReader: Can not initialize counter due to context is not a instance of TaskInputOutputContext, but is org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl
+-----------+
|myNewColumn|
+-----------+
|2D |
|2D |
|2D |
|2D |
|2D |
+-----------+
only showing top 5 rows
It looks like the udf function is invoked only once, isn't? I need a new random element in that column.
update 4 #user6910411
i have this actual code that increases the id but it is not concatenating the final char, it is weird. This is my code:
import org.apache.spark.sql.functions.udf
val mydf = sqlContext.read.parquet("some.parquet")
mydf.cache
def myNextPositiveNumber():String = monotonically_increasing_id().toString().concat("D")
val myFunction = udf(myNextPositiveNumber _)
val myNewDF = mydf.withColumn("myNewColumn",expr(myNextPositiveNumber))
scala> myNewDF.select("myNewColumn").show(5,false)
17/02/22 12:00:02 WARN Executor: 1 block locks were not released by TID = 1:
[rdd_4_0]
+-----------+
|myNewColumn|
+-----------+
|0 |
|1 |
|2 |
|3 |
|4 |
+-----------+
I need something like:
+-----------+
|myNewColumn|
+-----------+
|1D |
|2D |
|3D |
|4D |
+-----------+

Answer 1

Spark >= 2.3
It is possible to disable some optimizations using asNondeterministic method:
import org.apache.spark.sql.expressions.UserDefinedFunction
val f: UserDefinedFunction = ???
val fNonDeterministic: UserDefinedFunction = f.asNondeterministic
Please make sure you understand the guarantees before using this option.
Spark < 2.3
Function which is passed to udf should be deterministic (with possible exception of SPARK-20586) and nullary functions calls can be replaced by constants. If you want to generate random numbers use on of the built-in functions:
rand - Generate a random column with independent and identically distributed (i.i.d.) samples from U[0.0, 1.0].
randn - Generate a column with independent and identically distributed (i.i.d.) samples from the standard normal distribution.
and transform the output to obtain required distribution for example:
(rand * Integer.MAX_VALUE).cast("bigint").cast("string")

Answer 2

You can make use of monotonically_increasing_id to generate random values.
Then you can define a UDF to append any string to it after casting it to String as monotonically_increasing_id returns Long by default.
scala> var df = Seq(("Ron"), ("John"), ("Steve"), ("Brawn"), ("Rock"), ("Rick")).toDF("names")
+-----+
|names|
+-----+
| Ron|
| John|
|Steve|
|Brawn|
| Rock|
| Rick|
+-----+
scala> val appendD = spark.sqlContext.udf.register("appendD", (s: String) => s.concat("D"))
scala> df = df.withColumn("ID",monotonically_increasing_id).selectExpr("names","cast(ID as String) ID").withColumn("ID",appendD($"ID"))
+-----+---+
|names| ID|
+-----+---+
| Ron| 0D|
| John| 1D|
|Steve| 2D|
|Brawn| 3D|
| Rock| 4D|
| Rick| 5D|
+-----+---+